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Topic: Interface arduino up to 50 solenoids? (Read 1 time) previous topic - next topic

Valalvax


One last thing: I was looking for the resistors shown in the schematic.  I noticed that the resistor is rated 1k or 2.2k, however it appears that when I lookup resistors to purchase they come in 1k @ 1/4w, 1k @ 1w.  Some are metal film, some are carbon film..  What should I purchase? does the wattage and the film type matter?



Do you know Ohm's law?

P=IE

P = Power, measured in Watts (can also be VoltAmps)
I = Current, measured in Amperes or Amps
E = Voltage, measured in... erm... Volts... can't remember what the E stands for, it's one of the three different phrases that means Voltage..

So basically if you have a circuit with 5 Volts (the max voltage of the Arduino) you can have up to 200 milliamps with the 1W resister, or 50 milliamps with the 1/4 W

retrolefty


One last thing: I was looking for the resistors shown in the schematic.  I noticed that the resistor is rated 1k or 2.2k, however it appears that when I lookup resistors to purchase they come in 1k @ 1/4w, 1k @ 1w.  Some are metal film, some are carbon film..  What should I purchase? does the wattage and the film type matter?



It's very non-critical in value. It sets the base current value when turning on the transistor. Becaused of the very high current gain of that darlington transistor, it will saturate the transistor with either a 1k or 2.2k resistor. Any wattage rating you find will be more then enough running at the arduino ouput pin voltage of 5vdc. Carbon, metal film, they all will work fine in this simple switching application. Buy what's cheapest.

Lefty


rocketgeek

I sell an Arduino shield that does more or less exactly what you want. Sixteen high current DC outputs per shield, and it's designed to be daisy chained in groups of up to 25, for 400 outputs. http://www.logos-electro.com/ard-srg-ips4x4-1/. It will handle the voltage and current of the valve you linked with no problems at all.

Grumpy_Mike

Quote
the goal of being able to turn these devices on and off very fast.

How fast are we talking about here.
The problem with rapid switching of inductive loads is the time it takes for the current to rise in the coils. This is self limiting and the way round it is to use a higher voltage but then chop regulate it so the current stays within the limits. There is also a limit on how fast the solenoid will move given the mass, inertia, and applied magnetic force.

metrix

I want to be able to turn the valves on and off within a tenth of a second at times. Maybe I need to go with 120V valves and relays instead?

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