[Moved] Can I use a single Power Supply in a circuit with opto isolator ?

[milan.rajik]

Can I use a single Power Supply in a circuit with opto isolator ?

I am attaching the circuit. I need to control a optically isolated relay. The relay controls a motor. Relay Coil resistance is 144E. Relay is T92P7D52-12 tyco, 12V DPDT relay. The 12V power is given to relay circuit and also to a LM1117 to get 3.3V for Arduino Mini Pro 3.3V version. The 3.3V from LM1117 is given to 3.3V pin of Mini Pro. I have used a diode at collector of transistor to avoid induced back emf current while relay toggles. Will this work or should I use two different power supplies one for Mini Pro and one for Relay circuit ? I only need to avoid relay circuit hanging the Mini Pro.

 

[KlausST]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Hi,

you actually don´t have an optical isolation here because you refer to the same GND.

But it will work.

You can simplify your design just by connecting R1 to Q1.
U1, D9 and R2 is not needed.

Klaus

 

[milan.rajik]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Ok. I will test and reply.

 

[wp100]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Hi,

Yes, D9 is not needed, as D1 is the relay emf suppressor.

D10 also not needed because D3 already serves as a polarity blocker, unless you are deliberately using them to drop the input voltage ?

The led D2 will need its own dropper resistor.

R3 , was that intended to be D2s dropper but placed in the wrong location ? if not its probably going limit the current going to the relay coil, again simply remove.

As KlausST says there is little point in using an opto if using a common ground.
Using an isolator mean just that, no common connections at all.
Why are you wanting to use one anyway ?

Be careful when actually building with the lm1117, its pinout is different from most standard positive regulators and the metal tab is a Vout potential

 

[milan.rajik]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Yes R3 was a dropper for LED. Here is the new circuit. Will it work without hanging Mini Pro ?

 

[wp100]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Hi,

The circuit shown will work ok but its the load across the relay Contacts that may cause problems with Any micro.

To this end, if you get any reset problems etc, you should use suppressors across the contacts or motor body, if not already fitted.
What type of suppressors depends on the current/voltage and type of load, inductive or resistive.
You need to detail what your motors parameters are to get the correct advice.

Also see little point in using you own Lm1117 regulator when the Mini pro has its own inbuilt regulator; just feed the 9 -12v dc straight in to it.
You could put an extra 1000uf and 100nf cap at the input to the board.
The dc wires to the board should be twisted together.

Like any circuit, a well designed pcb and wiring will help minimise any noise pick up.

- - - Updated - - -

Hi,

I would use a simple circuit like this.

This site may also help
https://www.instructables.com/id/Connecting-a-12V-Relay-to-Arduino/step4/Calculating-R1/

 

[milan.rajik]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

My Mini Pro is ATMega 328P type.

 

[wp100]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

My Mini Pro is ATMega 328P type.

Hi,

Does that change anything ..?

Cannot see a Mini Pro with a 328 on the Arduino site, is yours a clone ?

Most boards , clone or not have an onboard regulator .. can you post a link to your boards and their schematics, saves everyone searching.

 

[milan.rajik]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Yes, mini is a clone. Here are the links.

**broken link removed**

**broken link removed**


I have given 12V supply to Vin pin. Can I take 5V from Vcc (5V) pin for TACT switches ?

Motor is connected to Relay output. It is a 1.5 HP pump, 230 V AC, 50 Hz, 1 phase.

 

[wp100]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Hi,

Thought you were running a 3v3 volt board ?

If its a 3v3 board where does 5v come from ?

Basically yes you can take the voltage for switches from the VCC line via a suitable resistor, providing you have one common voltage, not both.
If you are using one port for each switch then use a 10k pull up resistor.

https://arduino.cc/en/tutorial/button

 

[milan.rajik]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Sorry, Its a 3.3V board. Can I take 3.3V from Vcc pin for Tact switches ? Vin will be given 11.3V.

I am using 3.3V Mini Pro because there will be an XBee in the system. XBee will receive relay control commands from a remote control (Xbee Transmitter).

 

[wp100]

Re: Can I use a single Power Supply in a circuit with opto isolator ?

Sorry, Its a 3.3V board. Can I take 3.3V from Vcc pin for Tact switches ? Vin will be given 11.3V.

I am using 3.3V Mini Pro because there will be an XBee in the system. XBee will receive relay control commands from a remote control (Xbee Transmitter).

Hi,

Yes that should be fine, wired as show in that previous link.
With a 10k pull up resistor they take very little current.