Feedback on circuit design

Google Groups
1

Making a pretty simple switchboard circuit connected to a Raspberry Pi so I
can have a fun control panel thing. I’m pretty new to “proper” electronics

  • I can just about solder and “debug” some soldering problems, but my
    circuit design skills are a bit lacking. I did Physics A-Level and have
    done some logical circuit design at uni this year (in Verilog, making
    decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was hoping you
could give some advice/feedback - i.e. will this fry my Pi and do I need to
change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also input
to the GPIO so I can get the switch state in the software. I had no idea
what value to put for the pull-up resistors, but heard they were needed so
threw them in (they’re currently 100Ω http://en.wikipedia.org/wiki/Omega).
As a further complication, the switches I have are rated at 12V, but I
haven’t been able to test them at 5. Is this an issue, or I will need a 12V
supply and a transistor?

Thanks a lot,
Edward

2

Hey Edward,

The rating on switches is normally a maximum rating, you’ll be fine at 5v.

I’d suggest running the whole thing at 3.3v however, that way you can
dispense with the second set of resistors.

You might need to add pull down resistors, not sure if the pi gpio pins
have them built in.

Ta
BobOn 4 Sep 2014 23:10, “Edward Bennigsen” pe.ads0@gmail.com wrote:

Making a pretty simple switchboard circuit connected to a Raspberry Pi so
I can have a fun control panel thing. I’m pretty new to "proper"
electronics - I can just about solder and “debug” some soldering problems,
but my circuit design skills are a bit lacking. I did Physics A-Level and
have done some logical circuit design at uni this year (in Verilog, making
decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was hoping
you could give some advice/feedback - i.e. will this fry my Pi and do I
need to change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also input
to the GPIO so I can get the switch state in the software. I had no idea
what value to put for the pull-up resistors, but heard they were needed so
threw them in (they’re currently 100Ω http://en.wikipedia.org/wiki/Omega).
As a further complication, the switches I have are rated at 12V, but I
haven’t been able to test them at 5. Is this an issue, or I will need a 12V
supply and a transistor?

Thanks a lot,
Edward

–
You received this message because you are subscribed to the Google Groups
"Hackspace Manchester" group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

3

Edward,

This is the perfect time to learn how to use a circuit simulator! Software
specifically written to simulate how and electronic circuit will work -
very useful! There are even online versions that use java from within your
browser!

For free offline software check out LT Spice.

For the online one try

http://www.falstad.com/circuit/

They will show you whether your circuit will work how you expect.

I haven’t used the pi much for this sort of work but as bob said check if
the pi has internal pullup resistors on the gpio…if not the pull up
resistors need to be higher value - normally 10k R and if you use 3.3V the
current limiting resistor for the led is not needed.

Cheers

Alex

Hey Edward,

The rating on switches is normally a maximum rating, you’ll be fine at 5v.

I’d suggest running the whole thing at 3.3v however, that way you can
dispense with the second set of resistors.

You might need to add pull down resistors, not sure if the pi gpio pins
have them built in.

Ta
BobOn 4 Sep 2014 23:10, “Edward Bennigsen” pe.ads0@gmail.com wrote:

Making a pretty simple switchboard circuit connected to a Raspberry Pi so
I can have a fun control panel thing. I’m pretty new to "proper"
electronics - I can just about solder and “debug” some soldering problems,
but my circuit design skills are a bit lacking. I did Physics A-Level and
have done some logical circuit design at uni this year (in Verilog, making
decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was hoping
you could give some advice/feedback - i.e. will this fry my Pi and do I
need to change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also input
to the GPIO so I can get the switch state in the software. I had no idea
what value to put for the pull-up resistors, but heard they were needed so
threw them in (they’re currently 100Ω http://en.wikipedia.org/wiki/Omega).
As a further complication, the switches I have are rated at 12V, but I
haven’t been able to test them at 5. Is this an issue, or I will need a 12V
supply and a transistor?

Thanks a lot,
Edward

–
You received this message because you are subscribed to the Google Groups
"Hackspace Manchester" group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

You received this message because you are subscribed to the Google Groups
"Hackspace Manchester" group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

4

Thanks for the feedback! Glad to see I’m not too far from a decent circuit
:wink: I’ll change to 3.3V then and use the internal pull-up resistors, had
forgotten about those.

Thanks for the info about simulation, Alex. I’ve used Verilog at uni so
have had a fair amount of experience with testing circuits, but I didn’t
realise there were any decent free ones. I’ll have a look at the ones you
mentioned :slight_smile:

Thanks a lot,
EdwardOn 5 Sep 2014 07:26, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Edward,

This is the perfect time to learn how to use a circuit simulator! Software
specifically written to simulate how and electronic circuit will work -
very useful! There are even online versions that use java from within your
browser!

For free offline software check out LT Spice.

For the online one try

http://www.falstad.com/circuit/

They will show you whether your circuit will work how you expect.

I haven’t used the pi much for this sort of work but as bob said check if
the pi has internal pullup resistors on the gpio…if not the pull up
resistors need to be higher value - normally 10k R and if you use 3.3V the
current limiting resistor for the led is not needed.

Cheers

Alex

Hey Edward,

The rating on switches is normally a maximum rating, you’ll be fine at 5v.

I’d suggest running the whole thing at 3.3v however, that way you can
dispense with the second set of resistors.

You might need to add pull down resistors, not sure if the pi gpio pins
have them built in.

Ta
Bob
On 4 Sep 2014 23:10, “Edward Bennigsen” pe.ads0@gmail.com wrote:

Making a pretty simple switchboard circuit connected to a Raspberry Pi so
I can have a fun control panel thing. I’m pretty new to "proper"
electronics - I can just about solder and “debug” some soldering problems,
but my circuit design skills are a bit lacking. I did Physics A-Level and
have done some logical circuit design at uni this year (in Verilog, making
decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was hoping
you could give some advice/feedback - i.e. will this fry my Pi and do I
need to change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also
input to the GPIO so I can get the switch state in the software. I had no
idea what value to put for the pull-up resistors, but heard they were
needed so threw them in (they’re currently 100Ω
http://en.wikipedia.org/wiki/Omega). As a further complication, the
switches I have are rated at 12V, but I haven’t been able to test them at
5. Is this an issue, or I will need a 12V supply and a transistor?

Thanks a lot,
Edward

–
You received this message because you are subscribed to the Google Groups
"Hackspace Manchester" group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google Groups
"Hackspace Manchester" group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit
https://groups.google.com/d/topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

5

Just to clarify, did you mean I could get away with no current-limiting
resistors on the LEDs, Bob? I thought you always needed them so the LEDs
didn’t burn out.On Friday, 5 September 2014 08:47:20 UTC+1, Edward Bennigsen wrote:

Thanks for the feedback! Glad to see I’m not too far from a decent circuit
:wink: I’ll change to 3.3V then and use the internal pull-up resistors, had
forgotten about those.

Thanks for the info about simulation, Alex. I’ve used Verilog at uni so
have had a fair amount of experience with testing circuits, but I didn’t
realise there were any decent free ones. I’ll have a look at the ones you
mentioned :slight_smile:

Thanks a lot,
Edward
On 5 Sep 2014 07:26, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Edward,

This is the perfect time to learn how to use a circuit simulator!
Software specifically written to simulate how and electronic circuit will
work - very useful! There are even online versions that use java from
within your browser!

For free offline software check out LT Spice.

For the online one try

http://www.falstad.com/circuit/

They will show you whether your circuit will work how you expect.

I haven’t used the pi much for this sort of work but as bob said check if
the pi has internal pullup resistors on the gpio…if not the pull up
resistors need to be higher value - normally 10k R and if you use 3.3V the
current limiting resistor for the led is not needed.

Cheers

Alex

Hey Edward,

The rating on switches is normally a maximum rating, you’ll be fine at 5v.

I’d suggest running the whole thing at 3.3v however, that way you can
dispense with the second set of resistors.

You might need to add pull down resistors, not sure if the pi gpio pins
have them built in.

Ta
Bob
On 4 Sep 2014 23:10, “Edward Bennigsen” pe.ads0@gmail.com wrote:

Making a pretty simple switchboard circuit connected to a Raspberry Pi
so I can have a fun control panel thing. I’m pretty new to "proper"
electronics - I can just about solder and “debug” some soldering problems,
but my circuit design skills are a bit lacking. I did Physics A-Level and
have done some logical circuit design at uni this year (in Verilog, making
decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was hoping
you could give some advice/feedback - i.e. will this fry my Pi and do I
need to change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also
input to the GPIO so I can get the switch state in the software. I had no
idea what value to put for the pull-up resistors, but heard they were
needed so threw them in (they’re currently 100Ω
http://en.wikipedia.org/wiki/Omega). As a further complication, the
switches I have are rated at 12V, but I haven’t been able to test them at
5. Is this an issue, or I will need a 12V supply and a transistor?

Thanks a lot,
Edward

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send
an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google Groups
"Hackspace Manchester" group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit
https://groups.google.com/d/topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

6

Ed,

Here is a picture of what I think you should do:

[image: Inline images 1]

If you want to save on power and parts then use the internal pull down
resistor on the RPI gpio and use the 3.3 V output for the bus. If you do
that you can save energy. However purists would still fit a current
limiting resistor to the LED output and if using 3.3 V then 100R will be ok
to get the same level of brightness that you would get with 5 V and 220R.
However if you are trying to save time and costs then don’t fit the 100R
resistor. It will still work and I doubt anything bad would happen. If
after 10 years of use one of the LEDS failed short circuit you would blow
the GPIO output on the PI…not likely but could happen…

So to be doubly clear this is what you could do to save time and costs:

[image: Inline images 2]

Hope this clears things up for you.

Regards

AlexOn 7 September 2014 16:37, Edward Bennigsen pe.ads0@gmail.com wrote:

Just to clarify, did you mean I could get away with no current-limiting
resistors on the LEDs, Bob? I thought you always needed them so the LEDs
didn’t burn out.

On Friday, 5 September 2014 08:47:20 UTC+1, Edward Bennigsen wrote:

Thanks for the feedback! Glad to see I’m not too far from a decent
circuit :wink: I’ll change to 3.3V then and use the internal pull-up resistors,
had forgotten about those.

Thanks for the info about simulation, Alex. I’ve used Verilog at uni so
have had a fair amount of experience with testing circuits, but I didn’t
realise there were any decent free ones. I’ll have a look at the ones you
mentioned :slight_smile:

Thanks a lot,
Edward
On 5 Sep 2014 07:26, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Edward,

This is the perfect time to learn how to use a circuit simulator!
Software specifically written to simulate how and electronic circuit will
work - very useful! There are even online versions that use java from
within your browser!

For free offline software check out LT Spice.

For the online one try

http://www.falstad.com/circuit/

They will show you whether your circuit will work how you expect.

I haven’t used the pi much for this sort of work but as bob said check
if the pi has internal pullup resistors on the gpio…if not the pull up
resistors need to be higher value - normally 10k R and if you use 3.3V the
current limiting resistor for the led is not needed.

Cheers

Alex

Hey Edward,

The rating on switches is normally a maximum rating, you’ll be fine at
5v.

I’d suggest running the whole thing at 3.3v however, that way you can
dispense with the second set of resistors.

You might need to add pull down resistors, not sure if the pi gpio pins
have them built in.

Ta
Bob
On 4 Sep 2014 23:10, “Edward Bennigsen” pe.ads0@gmail.com wrote:

Making a pretty simple switchboard circuit connected to a Raspberry Pi
so I can have a fun control panel thing. I’m pretty new to “proper”
electronics - I can just about solder and “debug” some soldering problems,
but my circuit design skills are a bit lacking. I did Physics A-Level and
have done some logical circuit design at uni this year (in Verilog, making
decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was hoping
you could give some advice/feedback - i.e. will this fry my Pi and do I
need to change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also
input to the GPIO so I can get the switch state in the software. I had no
idea what value to put for the pull-up resistors, but heard they were
needed so threw them in (they’re currently 100Ω
http://en.wikipedia.org/wiki/Omega). As a further complication, the
switches I have are rated at 12V, but I haven’t been able to test them at
5. Is this an issue, or I will need a 12V supply and a transistor?

Thanks a lot,
Edward

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send
an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send
an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit https://groups.google.com/d/
topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google Groups
“Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

image.png719×662 9.76 KB

7

Wow, thanks for the comprehensive answer, Alex! I’ll probably go with the
last option as I’m timing out a bit. Out of interest, which package did you
use to draw the diagrams?

Again, thanks a lot!
EdwardOn 8 Sep 2014 11:09, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Ed,

Here is a picture of what I think you should do:

[image: Inline images 1]

If you want to save on power and parts then use the internal pull down
resistor on the RPI gpio and use the 3.3 V output for the bus. If you do
that you can save energy. However purists would still fit a current
limiting resistor to the LED output and if using 3.3 V then 100R will be ok
to get the same level of brightness that you would get with 5 V and 220R.
However if you are trying to save time and costs then don’t fit the 100R
resistor. It will still work and I doubt anything bad would happen. If
after 10 years of use one of the LEDS failed short circuit you would blow
the GPIO output on the PI…not likely but could happen…

So to be doubly clear this is what you could do to save time and costs:

[image: Inline images 2]

Hope this clears things up for you.

Regards

Alex

On 7 September 2014 16:37, Edward Bennigsen pe.ads0@gmail.com wrote:

Just to clarify, did you mean I could get away with no current-limiting
resistors on the LEDs, Bob? I thought you always needed them so the LEDs
didn’t burn out.

On Friday, 5 September 2014 08:47:20 UTC+1, Edward Bennigsen wrote:

Thanks for the feedback! Glad to see I’m not too far from a decent
circuit :wink: I’ll change to 3.3V then and use the internal pull-up resistors,
had forgotten about those.

Thanks for the info about simulation, Alex. I’ve used Verilog at uni so
have had a fair amount of experience with testing circuits, but I didn’t
realise there were any decent free ones. I’ll have a look at the ones you
mentioned :slight_smile:

Thanks a lot,
Edward
On 5 Sep 2014 07:26, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Edward,

This is the perfect time to learn how to use a circuit simulator!
Software specifically written to simulate how and electronic circuit will
work - very useful! There are even online versions that use java from
within your browser!

For free offline software check out LT Spice.

For the online one try

http://www.falstad.com/circuit/

They will show you whether your circuit will work how you expect.

I haven’t used the pi much for this sort of work but as bob said check
if the pi has internal pullup resistors on the gpio…if not the pull up
resistors need to be higher value - normally 10k R and if you use 3.3V the
current limiting resistor for the led is not needed.

Cheers

Alex

Hey Edward,

The rating on switches is normally a maximum rating, you’ll be fine at
5v.

I’d suggest running the whole thing at 3.3v however, that way you can
dispense with the second set of resistors.

You might need to add pull down resistors, not sure if the pi gpio pins
have them built in.

Ta
Bob
On 4 Sep 2014 23:10, “Edward Bennigsen” pe.ads0@gmail.com wrote:

Making a pretty simple switchboard circuit connected to a Raspberry Pi
so I can have a fun control panel thing. I’m pretty new to “proper”
electronics - I can just about solder and “debug” some soldering problems,
but my circuit design skills are a bit lacking. I did Physics A-Level and
have done some logical circuit design at uni this year (in Verilog, making
decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was
hoping you could give some advice/feedback - i.e. will this fry my Pi and
do I need to change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also
input to the GPIO so I can get the switch state in the software. I had no
idea what value to put for the pull-up resistors, but heard they were
needed so threw them in (they’re currently 100Ω
http://en.wikipedia.org/wiki/Omega). As a further complication, the
switches I have are rated at 12V, but I haven’t been able to test them at
5. Is this an issue, or I will need a 12V supply and a transistor?

Thanks a lot,
Edward

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send
an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send
an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit https://groups.google.com/d/
topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google Groups
“Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit
https://groups.google.com/d/topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

image.png719×662 9.76 KB

8

I used a combination of National Instruments Multisim for the Circuit
simulation and then Windows Paint as I haven’t got a box for RPI GPIO.

Cheers

AlexOn 8 September 2014 11:15, Edward Bennigsen pe.ads0@gmail.com wrote:

Wow, thanks for the comprehensive answer, Alex! I’ll probably go with the
last option as I’m timing out a bit. Out of interest, which package did you
use to draw the diagrams?

Again, thanks a lot!
Edward
On 8 Sep 2014 11:09, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Ed,

Here is a picture of what I think you should do:

[image: Inline images 1]

If you want to save on power and parts then use the internal pull down
resistor on the RPI gpio and use the 3.3 V output for the bus. If you do
that you can save energy. However purists would still fit a current
limiting resistor to the LED output and if using 3.3 V then 100R will be ok
to get the same level of brightness that you would get with 5 V and 220R.
However if you are trying to save time and costs then don’t fit the 100R
resistor. It will still work and I doubt anything bad would happen. If
after 10 years of use one of the LEDS failed short circuit you would blow
the GPIO output on the PI…not likely but could happen…

So to be doubly clear this is what you could do to save time and costs:

[image: Inline images 2]

Hope this clears things up for you.

Regards

Alex

On 7 September 2014 16:37, Edward Bennigsen pe.ads0@gmail.com wrote:

Just to clarify, did you mean I could get away with no current-limiting
resistors on the LEDs, Bob? I thought you always needed them so the LEDs
didn’t burn out.

On Friday, 5 September 2014 08:47:20 UTC+1, Edward Bennigsen wrote:

Thanks for the feedback! Glad to see I’m not too far from a decent
circuit :wink: I’ll change to 3.3V then and use the internal pull-up resistors,
had forgotten about those.

Thanks for the info about simulation, Alex. I’ve used Verilog at uni so
have had a fair amount of experience with testing circuits, but I didn’t
realise there were any decent free ones. I’ll have a look at the ones you
mentioned :slight_smile:

Thanks a lot,
Edward
On 5 Sep 2014 07:26, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Edward,

This is the perfect time to learn how to use a circuit simulator!
Software specifically written to simulate how and electronic circuit will
work - very useful! There are even online versions that use java from
within your browser!

For free offline software check out LT Spice.

For the online one try

http://www.falstad.com/circuit/

They will show you whether your circuit will work how you expect.

I haven’t used the pi much for this sort of work but as bob said check
if the pi has internal pullup resistors on the gpio…if not the pull up
resistors need to be higher value - normally 10k R and if you use 3.3V the
current limiting resistor for the led is not needed.

Cheers

Alex

Hey Edward,

The rating on switches is normally a maximum rating, you’ll be fine at
5v.

I’d suggest running the whole thing at 3.3v however, that way you can
dispense with the second set of resistors.

You might need to add pull down resistors, not sure if the pi gpio
pins have them built in.

Ta
Bob
On 4 Sep 2014 23:10, “Edward Bennigsen” pe.ads0@gmail.com wrote:

Making a pretty simple switchboard circuit connected to a Raspberry
Pi so I can have a fun control panel thing. I’m pretty new to “proper”
electronics - I can just about solder and “debug” some soldering problems,
but my circuit design skills are a bit lacking. I did Physics A-Level and
have done some logical circuit design at uni this year (in Verilog, making
decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was
hoping you could give some advice/feedback - i.e. will this fry my Pi and
do I need to change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also
input to the GPIO so I can get the switch state in the software. I had no
idea what value to put for the pull-up resistors, but heard they were
needed so threw them in (they’re currently 100Ω
http://en.wikipedia.org/wiki/Omega). As a further complication,
the switches I have are rated at 12V, but I haven’t been able to test them
at 5. Is this an issue, or I will need a 12V supply and a transistor?

Thanks a lot,
Edward

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it,
send an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send
an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit https://groups.google.com/d/
topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send
an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit
https://groups.google.com/d/topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google Groups
“Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

image.png719×662 9.76 KB

9

Ah cool, thanks!
EdwardOn 8 Sep 2014 11:21, “Alexander Lang” alexanderlang1980@gmail.com wrote:

I used a combination of National Instruments Multisim for the Circuit
simulation and then Windows Paint as I haven’t got a box for RPI GPIO.

Cheers

Alex

On 8 September 2014 11:15, Edward Bennigsen pe.ads0@gmail.com wrote:

Wow, thanks for the comprehensive answer, Alex! I’ll probably go with the
last option as I’m timing out a bit. Out of interest, which package did you
use to draw the diagrams?

Again, thanks a lot!
Edward
On 8 Sep 2014 11:09, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Ed,

Here is a picture of what I think you should do:

[image: Inline images 1]

If you want to save on power and parts then use the internal pull down
resistor on the RPI gpio and use the 3.3 V output for the bus. If you do
that you can save energy. However purists would still fit a current
limiting resistor to the LED output and if using 3.3 V then 100R will be ok
to get the same level of brightness that you would get with 5 V and 220R.
However if you are trying to save time and costs then don’t fit the 100R
resistor. It will still work and I doubt anything bad would happen. If
after 10 years of use one of the LEDS failed short circuit you would blow
the GPIO output on the PI…not likely but could happen…

So to be doubly clear this is what you could do to save time and costs:

[image: Inline images 2]

Hope this clears things up for you.

Regards

Alex

On 7 September 2014 16:37, Edward Bennigsen pe.ads0@gmail.com wrote:

Just to clarify, did you mean I could get away with no current-limiting
resistors on the LEDs, Bob? I thought you always needed them so the LEDs
didn’t burn out.

On Friday, 5 September 2014 08:47:20 UTC+1, Edward Bennigsen wrote:

Thanks for the feedback! Glad to see I’m not too far from a decent
circuit :wink: I’ll change to 3.3V then and use the internal pull-up resistors,
had forgotten about those.

Thanks for the info about simulation, Alex. I’ve used Verilog at uni
so have had a fair amount of experience with testing circuits, but I didn’t
realise there were any decent free ones. I’ll have a look at the ones you
mentioned :slight_smile:

Thanks a lot,
Edward
On 5 Sep 2014 07:26, “Alexander Lang” alexanderlang1980@gmail.com wrote:

Edward,

This is the perfect time to learn how to use a circuit simulator!
Software specifically written to simulate how and electronic circuit will
work - very useful! There are even online versions that use java from
within your browser!

For free offline software check out LT Spice.

For the online one try

http://www.falstad.com/circuit/

They will show you whether your circuit will work how you expect.

I haven’t used the pi much for this sort of work but as bob said
check if the pi has internal pullup resistors on the gpio…if not the
pull up resistors need to be higher value - normally 10k R and if you use
3.3V the current limiting resistor for the led is not needed.

Cheers

Alex

Hey Edward,

The rating on switches is normally a maximum rating, you’ll be fine
at 5v.

I’d suggest running the whole thing at 3.3v however, that way you can
dispense with the second set of resistors.

You might need to add pull down resistors, not sure if the pi gpio
pins have them built in.

Ta
Bob
On 4 Sep 2014 23:10, “Edward Bennigsen” pe.ads0@gmail.com wrote:

Making a pretty simple switchboard circuit connected to a Raspberry
Pi so I can have a fun control panel thing. I’m pretty new to “proper”
electronics - I can just about solder and “debug” some soldering problems,
but my circuit design skills are a bit lacking. I did Physics A-Level and
have done some logical circuit design at uni this year (in Verilog, making
decoders etc), but it’s all been a bit abstract so far.

Anyway, here’s a (not very neat) design for the switchboard, was
hoping you could give some advice/feedback - i.e. will this fry my Pi and
do I need to change anything :wink:

https://lh3.googleusercontent.com/-j5svUBW7r48/VAjiu6hfJ_I/AAAAAAAAAZ0/SEJmfFFkZdc/s1600/science_circuit_diagram_v1.png

The basic idea is that there’s switches which light up LEDs and also
input to the GPIO so I can get the switch state in the software. I had no
idea what value to put for the pull-up resistors, but heard they were
needed so threw them in (they’re currently 100Ω
http://en.wikipedia.org/wiki/Omega). As a further complication,
the switches I have are rated at 12V, but I haven’t been able to test them
at 5. Is this an issue, or I will need a 12V supply and a transistor?

Thanks a lot,
Edward

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it,
send an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it,
send an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in
the Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit https://groups.google.com/d/
topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google
Groups “Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send
an email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit
https://groups.google.com/d/topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to the Google Groups
“Hackspace Manchester” group.
To unsubscribe from this group and stop receiving emails from it, send an
email to hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

–
You received this message because you are subscribed to a topic in the
Google Groups “Hackspace Manchester” group.
To unsubscribe from this topic, visit
https://groups.google.com/d/topic/hacman/Lnw44mV2g68/unsubscribe.
To unsubscribe from this group and all its topics, send an email to
hacman+unsubscribe@googlegroups.com.
To post to this group, send email to hacman@googlegroups.com.
Visit this group at http://groups.google.com/group/hacman.
For more options, visit https://groups.google.com/d/optout.

image.png719×662 9.76 KB