Circuit Review

s1buell over 7 years ago

I`m currently making some proto circuits and I would love some feed back/Ideas etc.

All these circuits will connect to Arduino or Arduino compatible devices.

Anyone have time to help out with some reviews?

First circuit is a 4-20ma board

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genebren over 7 years ago in reply to s1buell +4

You might need to modify your 4-20ma loop front end somewhat. First, the circuit as shown does not have a return path for the current loops. Also, the current loop may not necessarily be directly referenced…
genebren over 7 years ago in reply to s1buell +4

Tom, Again, I am not sure that you can count on the second leg of the 4-20ma loop to be at ground potential. You might end up shorting out a driver or introducing ground noise into the circuit. Here is…
genebren over 7 years ago in reply to s1buell +4

Tom, Here is an even better link. This shows how to differential sense the loop current. https://www.sensorsmag.com/components/implementing-a-4-ma-to-20-ma-sensor-interface Good luck! Gene

s1buell over 7 years ago in reply to genebren

Yes agree. I reviewed the worst-case spec`s (13VDC upper end for example) and then put the TVS inside these specs to save the components. I really like these TVS diodes they are an easy way to protect bus side of the solution.
So, do you think its worth keeping the optical chips?
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s1buell over 7 years ago

BTW Have a good weekend! Its time for a cold cold cold beer!!!!

cheers
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genebren over 7 years ago in reply to s1buell

Tom,

Strange, but I had replied earlier, and stated that I think you should leave out the Optoisolators. They really are buying you and protection given that the transceiver is now protected nicely. About the only time I would use the optoisolators is if the transceiver was power by an isolated DC-to-DC supply, or if there was a high voltage source nearby (on the other side of the 485 bus).

Good job!
Gene
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genebren over 7 years ago in reply to s1buell

Tom,

Thanks! I'll have a cold one also.
Gene
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s1buell over 7 years ago
Agree. I don’t see the need now for the optical. I have the power side covered well I think....

Here is the final RS485
I’m going to post the RS232 for you to have a quick look
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s1buell over 7 years ago

RS232 with TVS protection

I used .1uF Tant at 3.3VCD power input. Now the manual says to use a different config but everything I read and every circuit I see is using this config at 3.3VDC.

Have a look.
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genebren over 7 years ago in reply to s1buell

Tom,

Typically the bypass capacitor (in this case C5) does not need to be a tantalum. I usually just use a ceramic. Otherwise, this looks good.

Gene
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s1buell over 7 years ago

Gene you have time to check out a 12V DC power supply with reverse polarity/surge protection?
I need a second pair of eyes.....
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genebren over 7 years ago in reply to s1buell

Tom,

Sure, post it and I'll review it.

Gene
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s1buell over 7 years ago in reply to genebren

U2 & U3 are the protection circuit.
U7 is a simple 12vdc regulator for 12VDC connections
U1 is my 12VDC dual output source
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