Developing a system using a microcontroller to read temperature to activate pumps and servos

Being a manufacturing engineer, I do not have the knowledge yet to develop an electronic system as such. If anyone can help recommend some products that can achieve this goal it would be greatly appreciated.
My Process: I take a mixture of citric acid and reverse osmosis water and heat that solution to about 180 degrees F. After the solution has been heated, I plum in a heat exchanger and through several valves run that mixture through the heat exchanger to passivate the metal.
What I need: I want a microcontroller to be able to turn on and off our heating element of the mixture based on a thermostat reading plus a digital readout of said temperature. Once the solution has been heated to a desired temperature, we want that controller to be able to activate our water pump (120V). Indicator lights for the heat element and the pump. Next, a flow sensor to ensure that the pump is not running dry. A physical on/off switch to boot the controller. Two emergency stop switches, one near the operator and another one closer to the passivation station (within 5 ft of microcontroller). Hour meter to show how long the heating element has been activated. Hour meter to show how long the water pump has been running. Eventually we would like to have the microcontroller be able to activate servos to open and close the valves. All these sensors must be able to handle an acidic solution.

Thanks for taking your time to read this post. Again, all recommendations are very much appreciated.

Welcome to the DigiKey TechForum SuperCoils.
This should be answered by one of the engineers, as they have a lot more knowledge about designing the system. Hopefully one of the engineers can comment on this post.

Hello SuperCoils.

This is my understanding of your needs including future expansion:


  • digital: tank full
  • digital: tank empty
  • digital: flow sensor
  • digital: auto-off-manual selector switch
  • digital: manual start process selector switch
  • analog: tank temperature
  • analog : pH


  • digital: heater (120 VAC assumed)
  • digital: pump (120 VAC)
  • digital: water fill solenoid (120 VAC assumed)
  • digital: acid fill solenoid (120 VAC assumed)
  • digital: empty solenoid (120 VAC assumed)
  • digital: on indicator lamp
  • digital: fill indicator lamp
  • digital: temperature increasing
  • digital: passivation in process


  1. The emergency stop mechanism shall be independent of the PLC or microcontroller. Recommend a safety relay:
  1. The system would benefit from a Human Machine Interface (HMI) as this would simplify the user interactions. It would also provide a way of adjusting the various setpoints and provide a home for the hour meters.

Based on this understanding, may I recommend you use a Programmable Logic Controller (PLC) as your system falls clearly in the realm of industrial controls. You will find that the building blocks for your desired sensors and actuators fit hand in glove with the PLC. For example, appropriate analog sensors will be designed to connect directly to the PLC or a PLC expansion module. Likewise, relays to control the pump and heater are readily available and easily connect to the PLC.

None of this suggest that you can’t use a microcontroller. However, consider that the heart of a PLC is a microcontroller surrounded by hardened interface circuitry. This is circuitry that you would otherwise need to custom design yourself.

As for selecting a specific PLC, the link below narrows down the DigiKey offerings. Recommend:

  1. refine your requirements with room for expansion.
  2. cross this with the previous link to match a PLC with an HMI
  3. consider a PLC that is IEC 61131-3 compliant as this appears to be a growing trend in PLC programming
  4. consider hiring a PLC system integrator to help get you started

Please let us know if we can provide additional assistance.

Best Wishes,


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