Professor Rob gives you an A, there would have been a + but you crossed out partially with something I can't quite make out.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“.
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.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.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
True, that is actually quite a nice way of doing it.
