TinyIOx PMW out safe voltage range

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TinyIOx PMW out safe voltage range

Postby jsiedlicki » Fri Mar 02, 2018 10:56 pm

I want to drive a solid state relay using generic PWM with Timer2 channel 0. The specs for the relay state the PWM input voltage range is 3.5 - 32 VDC. What can the TinyIOx safely sink on the PWM out channels?
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Re: TinyIOx PMW out safe voltage range

Postby jbelanger » Fri Mar 02, 2018 11:11 pm

All the I/O pins are limited to 0-5V. But the main issue here is the current capability of the I/O pins and their vulnerability to outside signals.

For all output pins, you need to have some sort of driver circuit to activate outside components such as a SSR. In this case, you will need to use a small transistor and a current limiting resistor. A 1k resistor with a PN2222 transistor will easily drive the SSR. You can connect 12V to the + side of the SSR and the - side of the SSR to the transistor similar to the relay output circuit on this manual page (you can omit the diode with an SSR).

Jean
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Re: TinyIOx PMW out safe voltage range

Postby jsiedlicki » Sat Mar 03, 2018 9:14 am

Thank you for the fast response.

A few more questions. Sorry if these seem silly, but I'm not an electronics guy :lol:

In the custom box I made to house the TinyIOx I only have access to 5Vref and sensor ground from my MS3-Pro. So should I build the driver circuit you mentioned outside the box, near the SSR, which has access to 12V power and chassis ground? Or can I build the circuit inside the box using 5Vref and sensor ground instead? Just for reference, the SSR I am using draws a maximum input current of 15mA to trigger the relay according to their specs sheet.

I am assuming it is not good to ground a 12V signal thru the sensor ground.

John
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Re: TinyIOx PMW out safe voltage range

Postby jbelanger » Sat Mar 03, 2018 2:30 pm

You're correct that grounding the 12V signal to the sensor ground is not a good idea. And while 15mA is not a lot so that could be acceptable for Vref, a PWM signal is definitely not something you want on either Vref or the sensor ground. Since it goes on and off very rapidly, that will create noise on your other sensors signal. And you don't want to put the driver circuit outside the TIOx box because it also has a function of protecting the CPU from outside signals.

Since you need to bring in a wire for the SSR trigger, can't you also bring in a ground wire? Those are the only things you need to bring in; the 12V only goes to the SSR. And the ground doesn't have to come from a specific place but can be from any good ground location and the wire can be quite small since it will be a very small current. So you would have the 1k resistor and transistor inside the box with the resistor connected between the TIOx output and the transistor and the SSR trigger and ground wires connected to the transistor.

Jean
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Re: TinyIOx PMW out safe voltage range

Postby jsiedlicki » Sat Mar 03, 2018 3:08 pm

Thank you Jean. I will bring in the SSR trigger and chassis ground wire to complete the circuit.
You are quite patient and always explain things very thoroughly. Quite helpful for the inexperienced like myself.

BTW, I love your TinyIOx product, I am using all 9 ADC's and will be using both PWM outs soon!
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