Controlling 0-5.7v signal dc motor

Completely disconnected. Circuit is sitting on my desk. I have checked the voltages and I have 5.7v across the 5k pot and 12v across -ve MIN to +ve MAX pot - same as other controllers.

However, I checked VR3 (the pot coming off the wiper on the analogue pot) and it is not measuring any voltage across it's terminals whilst the on the other controllers it has a min 0.5v and increases with voltage from wiper. Maybe D9 has blown.

Did you check if the original pot was full-travel?

Hi Mark. I somehow blew a diode on the circuit off the 1-5v wiper. Replaced it and it all works as per usual.

After pulling my hair out it looks like I have finally gotten it to work. I am powering the opamp side off the circuit from the controller and feeding back variable voltage to the DC using a pwm signal (ironically via an analogue pot - for testing only) out of the arduino.

What is the story with grounds potential here? Is there any way that the mains potential can leak over to the arduino side? I will be powering the arduino via it's own power supply but off the same mains source as the DC controller.


If you construct your circuitry to keep each side of the opto-coupler circuit apart you should be fine.
Most optos have 1000V or higher isolation.

Tom... :smiley: :+1: :coffee: :australia:

This is called clearance and creepage distances - this is essential.

1000V insulation is not safe for mains. Mains transients due to lightning and switching fridges etc have to be allowed for, and safety factors are applied to allow for aging and moisture, typical optoisolators should have proof voltages that are multi-kilovolt (4kVrms is typical). You need to check the creepages/clearances for your mains voltage and regulations, ditto the reinforced insulation proof voltages.

If in doubt don't take risks with mains.

Typical photonic barrier isolation is 5000V, not 1000V.

Opto isolator datasheet

"Isolation test voltage
between emitter and detector t = 1 s VISO 5300 VRMS"


@TomGeorge is right then.. 5300 > 1000.... :smiley:

Tom... :smiley: :+1: :coffee: :australia:
PS. Sorry in a sarcastic mood.. :+1: :+1:

Really ?
You mean they still allow sarcasm on the Forum ?

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Sarcasm aside, thanks for everyone in a giving me a hand/information. Much appreciated.