I have 10 valves that require between .8 and .975 volts with a current draw of 750mA. I was hoping to use the PWM ports of my Arduino MEGA but the current requirement isnt going to allow me to do it. Any idea of the type of circuit I'd need to build?
I'm a CS guy and this whole EE stuff is a touch over my head.
Any help would be greatly appreciated.
That's a very strange and unusual voltage requirement for a valve. Do you have a link to a data sheet for it?
It is an Nitinol based Electrostem Valve.
Here is the datasheet for it:
very interesting valve, I've never seen something so small yet able to handle significant air pressure.
The easiest way to drive these I think would be to utilize a logic level N-channel MOSFET switching transistor for each valve controlled.
The Arduino PWM output pin would wire to the gate of the mosfet. The source of the mosfet would wire to ground the drain of the mosfet would wire to one terminal of the valve. The other valve terminal would wire to a series connected current limiting resistor and the other end of the resistor would wire to a new external +5vdc power supply. The new supply ground wire would have to wire to both the ground terminal of the arduino and the mosfet source terminal.
The resistor should be sized to allow a maximum of 750 ma or around 5.5 ohms and be of 5 watt size of better. You should also wire a pull down resistor of say 4.7k ohms from the Arduino output pin to ground to insure that the valves stay closed if the Arduino chip is turned of or reset while the external +5vdc power supply is still turned on.
The last spec you need is how much current does the new external power supply need to have. Worst case is around 10 amps if all valves are needed to be on at 100% continuously. Less if only a few are on at a time or they are operated in sequence.
retrolefty, thank you for your much appreciated input. I am also using this valve in a similar setup and got it working on my own, but electronics newbs operate in a fog...
A) attaching leads to the valves is awfully finicky, and the supplied fuse holders don't really hold anything well. Anyone have ideas?
B) I am using Darlington transistors with 3V at the collector (did it with 4.5 up to 6V at first). Is that notably worse than a MOSFET, and if so, in what way?
C) I should be able to use the 3.3V output of a PC power supply to drive a couple of valves simultaneously, right?
These valves really are interesting!
Is that notably worse than a MOSFET, and if so, in what way?
Yes because when the transistor is on conducting the full current there will be a 1 to 2V drop across it. This will be dissipated in heat. The on resistance of a FET produces a very much lower voltage drop and so less heat. Too much heat will destroy the device.
I should be able to use the 3.3V output of a PC power supply to drive a couple of valves simultaneously, right?
Yes - remember to connect the ground of this powersupply to the ground of the arduino.
Thank you Grumpy_Mike!
To be precise, I of course fed the valve its recquired 0.95 V. It seemed silly to burn off so much of a voltage difference, which is why I'm trying to go with 3.3V.
Hey Chris i just bought 10 valves the same model than the ones you are using, i already have a circuit to use them, but i don't know how to connect them i really dont understand the data sheet, can you help me please?