Are there any unused pins on the Arduinos?

Continuing the discussion from Purpose of 'Acknowledge' Command:

After a bit more finagling, I was able to get my LED to turn off before taking OD and then turn back on after. Success!

In a similar way, I want to turn off pumps that I’ll be using to bubble air into the culture.

I’m assuming that I need to minimize lag time with the whole on/off routine, so I need to control these pumps using the same Arduino that does OD and light. Otherwise I would have these pumps on the fluidics module and have a communication with the system there.

I’d be controlling the pumps (which run off of wall AC) via a relay, so that the 12V eVOLVER architecture could turn them on and off.

Therefore I see two options:

  1. Plug the relay/pumps into the circuit that’s controlling the light.

    • So the PWM for the light pin on each vial would run 1) an LED and 2) a relay that powers a pump
    • I tried this in parallel to minimize voltage drop in the LED and it worked
    • BUT it burnt out my relay because when the LED turns back on the voltage spikes to 16
    • Another problem is that I want to be able to run the LED at anywhere between 6V and 12V to produce a variety of different light intensities. So a potential relay would need to be able to 1) withstand 16V spikes 2) turn on between 6 and 12V… This seems unlikely to be thing on its own
    • Therefore I’m thinking that I could use a voltage regulator to keep the voltage at constant 6 volts regardless of input
    • However, any changes in the relay circuit would affect the LED? Not sure about this…
  2. The simpler option? Run the relay off of one of the pins on the arduino

    • The Arduino can output a constant voltage :heavy_check_mark:
    • Don’t have to have 16 relays :heavy_check_mark:
    • No affecting LED values :heavy_check_mark:
    • No delay :heavy_check_mark:

My question: are any of the pins on the Arduinos not being used by the two sub-boards? I can’t seem to find current layout of the motherboard on the github

I would also love general design feedback on solving this problem because I’m really just starting to learn electronics.

Thanks in advance for any help!

Hi Nate,

Can you post a simple schematic of what your setup looks like? I’m not sure if I totally understand what you are describing here.