Running five devices off an Arduino simultaneously using MOSFET and SSR

Projects General Guidance
1

My project involves two MOSFET controlled DC motors and two SSRs. I have external power supplies for each of the four devices. I have been able to operate and control all four devices independently.

Here's where I'm stuck. The Arduino Uno max output is 5V, so I don't see a way to control these four devices (plus a temperature sensor) simultaneously unless I'm misunderstanding something.

I understand that with multiple channel mechanical relays like the one below, you can use three power supplies: the arduino board gets power from USB or external supply, relay board can have a separate power supply, and the device being used with the relay has a power supply.

Is something like this possible with SSR and MOSFET? Can anyone point me in the right direction for getting these four devices (five with the sensor) running together?

2

I'm not sure I follow (but others with more experience will be here shortly.. I'm sure!) :slight_smile:

But..

You wouldnt 'power' anything from the Arduino.. IMO..

You are just using the Arduino as a 'trigger' to toggle the SSR's or the MOSFET's..

3

If You use logic MOSFETs it will work. I use an SSR and without any problem.

4

xl97:
You wouldnt 'power' anything from the Arduino.. IMO..

You are just using the Arduino as a 'trigger' to toggle the SSR's or the MOSFET's..

Yep, you are right, I'm not trying to power the devices with the Arduino, which is why I have four separate power supplies. I am using PWM with two MOSFET and two SSR which I have been able to work independently just fine.

The issue is that all of these devices require some amount of voltage (e.g. SSR needs 3V minimum to trigger) including the sensor. I don't know how to use all five devices at once when the Arduino can only supply 5V.

Again, maybe I have a misunderstanding, but from what I understand, the Arduino would not be capable of providing the voltage needed to operate all five devices (two SSR, two MOSFET, one sensor).

5

Railroader:
If You use logic MOSFETs it will work. I use an SSR and without any problem.

Doesn't the SSR require 3V minimum and the Arduino can only provide 5V total? How does this work when you have all four operating at once?

I feel like I'm misunderstanding something here.

6

What are You bubbling about, 5 volt is not enough for an SSR needing only 3 volt to trigger?
Attach a wiring diagram!

7

Railroader:
What are You bubbling about, 5 volt is not enough for an SSR needing only 3 volt to trigger?
Attach a wiring diagram!

I didn't say 5V isn't enough to trigger an SSR requiring 3V. I said I don't think 5V is enough to trigger four devices, each require several volts to trigger (plus a sensor).

Wiring diagram? It's just a simple setup like below but with the other SSR and two MOSFETs controlled by a separate PWM pin. I don't think a full wiring diagram is necessary for this question.

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I'm not sure you understand what I'm asking. I'm trying to operate multiple SSRs and multiple MOSFETs at the SAME time. Each requires a base voltage, right? So if that total voltage exceeds to 5V max of the Arduino, how would I go about using them simultaneously?

8

If you connect 3v a device to a +5v power source... it doesnt mean you have only 2v left.. (is that what you are saying?)

9

Again, attach a diagram showing how You have planned to connect the devices to the Arduino. Your arguments makes no sense.

10

xl97:
If you connect 3v a device to a +5v power source... it doesnt mean you have only 2v left.. (is that what you are saying?)

So, I can draw 5V across each pin as long as I don't exceed a total output current of 0.5 A, or 0.04 A across any individual pin?

11

You don't "draw volts", You draw current, milliAmps. There You are correct. You need to sum up the current delivered by the OUPUTs. Max per pin is, for an UNO, 20 mA but You can't output 20 mA on all the digital outputs at the same time.

12

Thank you for the explanation.

Railroader:
but You can't output 20 mA on all the digital outputs at the same time.

Is this just because you're drawing too much total current? If you have 5 pins drawing 20 mA, this would total 100 mA which should be safe, right?

All my output pins are drawing under 20 mA, I'm just wondering.

13

Check the spec for Your controller for the total maximum output current. A logic MOSFET consumes microAmperes and the SSR very little current so You will be safe.