Controlling SSR for 3D printer heater

I'm looking for a solution to adapt my CNC mill to 3D printing.
The machine is already a 3 axis controlled by a 7i47 and sensors by a 7i84.
I read something related HAL PID for temperature controller.

My question is about the 7i84 that I would like to use to control the SSR to switch current from power supply to the heater.
Can I connect directly a 7i84 output to a SSR? do I have to put some resistor?
If I use the 7i84 can I use PWM to control the SSR? The other point is if it is possible to control SSR using PWM.
The other idea is modified the HAL that implement the PID to use 0 or 1 as PID output and not a range of values to implement PWM.

Someone have any idea to reuse the mesa cards to implement PID for heating?

gandalf wrote:

I'm looking for a solution to adapt my CNC mill to 3D printing.
The machine is already a 3 axis controlled by a 7i47 and sensors by a 7i84.
I read something related HAL PID for temperature controller.

My question is about the 7i84 that I would like to use to control the SSR to switch current from power supply to the heater.
Can I connect directly a 7i84 output to a SSR? do I have to put some resistor?
If I use the 7i84 can I use PWM to control the SSR? The other point is if it is possible to control SSR using PWM.
The other idea is modified the HAL that implement the PID to use 0 or 1 as PID output and not a range of values to implement PWM.

Someone have any idea to reuse the mesa cards to implement PID for heating?

typically a SSR have a wide range off input voltage to enable it. the mesa 7i84 in short terms outputs his supply voltage. So you need to see it that SSR accepts this level of voltage. But is highly probable that it will work.

You can use a pid component, convert in pwm and associate it to one 7i84 output.

see the PWM component:

linuxcnc.org/docs/html/man/man9/pwmgen.9.html

Its likely that you have to use a low frequency, 1Hz cycle should be fine.

I choose for another way.
I think to buy a external PID temperature controller.
With some models It is possible to manage the controller using modbus over rs485 or control inputs (normally open contacts).
I think I will go for a PID controller without rs485 port.
The model I choose has 3 control inputs (for START/STOP, ...), some alarm output (to check if temperature target is reached) and a transfer output that with a 0-5V output It is possible to read the temperature from the thermocouple.
In this way I can make a pyVCP to start, stop and monitor the temperature.

Initially I will try to read the analog output voltage from the PID controller using the 7i84 ADC that is not very accurate 8 bit on 36V range.
In this way I will have an error on temperature reading in AXIS but should be enough to monitor the PID controller because I will use the alarm output to check if the range target temperature is reached.