DIY Doser run on digital electric input

[Sral]

I soldered everything up and connected the wires. I won’t test the PWM dimming for now, since that’s bound to only reduce the motors’ lifetime:

Maybe I shouldn’t have tried to squeeze everything in this box, but hey, it seems to have worked ^^

 

[robsworld78]

Ah, great, that means my electronics "knowledge" hasn't failed me. Even if is is 12V PWM, as long as it works, it's fine ^^

Another thing I noticed: if you measure this, the load together with the stray capacitances will probably impact the waveform of the 12V PWM, depending on the actual load impedance, inductance and capacitance involved. That way you might get different results from measuring directly with a multimeter/oscilloscope (high impedance) or with an actual load (a 1k resistor being comparatively "low impedance" or a DC motor that is even lower impedance with additional inductance).

Additionally I had a go at calculating the sh** out of a DC motor run at different DC voltages. It rurns our that one has to account for the fact that the load is not linear with the water flow,e.g. double the water flow requires a bit more than double the power, similar to air drag in a car. Otherwise the current draw at 5V and 12V would need to be the same for identical loads, but running slower at 5V.
This is the result:

As you can see the formulas reproduce the measured performance in the top right corner very well.

Simply measure winding resistance with a multimeter, stall voltage with an adjustable power supply and current draw at nominal voltage and you can calculate the performance change at different DC voltages. Flow is proportional to motor frequency. Motor frequency is proportional to voltage above the stall voltage. Current also increases linearly with voltage, but increases slower as soon as the motor starts moving, where the current is equal to V_stall divided by winding resistance.

Mind that this only holds true for DC voltage, or DC voltage with a limiting resistor (you’ll probably have to use the sum of R_motor and R_limit in the formulas) not for a PWM drive.

Although thinking about it, it might actually be very similar for PWM at a constant frequency, just with a higher „stall duty cycle“ instead of a „stall voltage“.

Professor Rob gives you an A, there would have been a + but you crossed out partially with something I can't quite make out.

 

[Sral]

Another thing I have noticed:
does anybody know how well dosing with Timers and Equipment works or is there a way to use the doser tab to run equipment ?

With my current 5V drive I should have about 0.5ml / second which sounds rather ideal for an integer amount of runtime in seconds

 

[robsworld78]

Another thing I have noticed:
does anybody know how well dosing with Timers and Equipment works or is there a way to use the doser tab to run equipment ?

With my current 5V drive I should have about 0.5ml / second which sounds rather ideal for an integer amount of runtime in seconds

If you're happy with running a pump for say 5 seconds you could use a timer, have it turn on and X number of seconds later turn off. Using the dosing tab might be more accurate though, if you drive your circuit with a PWM pin you can use it. The lights and dosing tabs work with Jack connectors which is any PWM pin and the equipment, ato and timer tabs work with Outlet connectors. You can setup a standard GPIO or PWM as an Outlet but Jack connectors only work with PWM pins.

 

[Sral]

If you're happy with running a pump for say 5 seconds you could use a timer, have it turn on and X number of seconds later turn off. Using the dosing tab might be more accurate though, if you drive your circuit with a PWM pin you can use it. The lights and dosing tabs work with Jack connectors which is any PWM pin and the equipment, ato and timer tabs work with Outlet connectors. You can setup a standard GPIO or PWM as an Outlet but Jack connectors only work with PWM pins.

Thanks !
I’ll use timers then. Should be easy to set up although calibration might be a little hard with only 1 s steps. I’ll test this and get back to you.

 

[Ranjib]

Another thing I have noticed:
does anybody know how well dosing with Timers and Equipment works or is there a way to use the doser tab to run equipment ?

With my current 5V drive I should have about 0.5ml / second which sounds rather ideal for an integer amount of runtime in seconds

I exclusively use timer for dosing. I found that to be most optimum and offload the direction/speed control on a physical knob/ circuit that’s not under reef-pi control.
something like this: https://a.co/d/dMHc7Lh

 

[Sral]

I exclusively use timer for dosing. I found that to be most optimum and offload the direction/speed control on a physical knob/ circuit that’s not under reef-pi control.
something like this: https://a.co/d/dMHc7Lh

True, that is actually quite a nice way of doing it.

That also got me thinking. I can very easily adjust the individual motors using a very small inline resistance of up to 2 ohm or so. That would then see a maximum of 0,25 W, but allows me to trim all motors to about the same speed. It also has the upside of not needing a PWM that could potentially decrease motor lifetime.