Finally I finished the second version of my circuit which should control different solenoids.

You can view the large version here.

enter image description here In particular, this circuit should control 2 proportional solenoids and 7 ON/OFF solenoids.

The solenoids parameters are: V = 12Vcc, R = 3.7 Ohm, I = 1.80A

In order to prevent an atmega328p reset due to noise (like it happened in the first version), I added:

As suggested in the application note of its datasheet, I used an inductor L1-1UH with a capacitor for the THL-25 input. Is it OK?

In this way, I have two different grounds, GND5 is the gnd for 12V, while GND is the ground for 5V . I also added a big 2200uF capacitor between +12V and GND5 in order to avoid noise. The capacitor C5 100nF is OK for the atmega328p? I will place it very close to the atmega pins.

The output named "OUT5/SERVO PWM" should control a 12V, 4A RC servo.

Is there any error in my schematics?

Anything to improve?

The big C3 capacitor is enough for the filtering?

The circuit close to the isolated power supply is correct?

Can you help me, please?

I would like to improve my circuit, if possible.

Thank you for your support and your help!

EDIT1: I updated my schematics by adding the SERVO connections and pinout. EDIT2: I changed the SERVO circuit by using a P-mosfet. This is the SERVO schematics.

EDIT3:: This is the new schematics for the servo controlling.

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    \$\begingroup\$ Have you read AVR042 yet? \$\endgroup\$ Nov 17, 2016 at 22:07
  • \$\begingroup\$ I used the official connections for the atmega328p, as reported on the arduino documentation, too. Are they wrong? \$\endgroup\$ Nov 17, 2016 at 22:09
  • \$\begingroup\$ Haven't actually looked yet. I'm multitasking ATM. \$\endgroup\$ Nov 17, 2016 at 22:09
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    \$\begingroup\$ Why do you think you need to use both an optocoupler and a MOSFET driver here? \$\endgroup\$
    – user39382
    Nov 17, 2016 at 22:13
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    \$\begingroup\$ I just want to be sure that the atmega will be fully isolated from the high power lines.. is it not correct? \$\endgroup\$ Nov 17, 2016 at 22:35

1 Answer 1


enter image description here

  • The area in Yellow needs to be fixed as PWM will not work.

  • Dont you want to put a cap on RESET to gnd for POR?

  • How far are all the cable interfaces?

  • What type of shielding do you need?
  • Do you have a functional spec for immunity?

  • Are you planning to do Susceptibility testing? Radiated Arc, Impulse RF , Induction spikes etc.... if so what is your spec for dV/dt , dI/dt or field strengths for crosstalk from load to inputs etc.

  • if you dont make a spec, how will you know it wont fail? or when it will fail

    • or if it is interface overkill./..\

It's like an architect who designs a bridge with elastomers and even tension supports and forgets about wind effects. If you dont define all the environmental risks, how can you say it passes?

  • \$\begingroup\$ I updated the schematics by adding the SERVO connection. I didn't understand your first three points and neither your drawing. Can you please let me know if the updated schematics is clearer? The servo is OK, now? Thank you! \$\endgroup\$ Nov 18, 2016 at 10:10
  • \$\begingroup\$ there is an error in yellow, sorry, was trying to be funny, \$\endgroup\$ Nov 18, 2016 at 13:30
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    \$\begingroup\$ Ki Servo pin 2 should go to D7-Anode if Servo is active LOW, otherwise Q6 is blocked by reverse biased D7 \$\endgroup\$ Nov 18, 2016 at 13:51
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    \$\begingroup\$ is servo some low side switch with pullup or highside switch with R to gnd? if inductive cable, high side turn off makes a negative spike so D7 cathode moves from V+ to Servo PWM input to clamp neg. spike to -0.7, , if low side switch with pullup move as indicated in my dwg \$\endgroup\$ Nov 18, 2016 at 19:18
  • 1
    \$\begingroup\$ google.ca/… \$\endgroup\$ Nov 19, 2016 at 17:45

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