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2 projects 13 followers
Update a devices wifi configuration from your phone
Craig Mulligan and Pablo Carranza Vélez
A safe-deposit box that requires 2FA to open. Built with resin.io and Authy.
Receive SMS sent to a Twilio number and then convert them into audible speech with google text-to-speech, on your Raspberry Pi.
A toilet queueing app for serious poopers. Uses resin.io, firebase and twilio to notify people when the toilet is open - runs on the RPI.
More on the diode: https://en.wikipedia.org/wiki/Flyback_diode
Matt, that's some nice research you're doing :)
Indeed, I used three 10 ohm resistors to get 3.3 ohms, since I didn't have higher power resistors at hand and using them in parallel raises the max current they can handle.
Sorry I missed the 100k on the list :S
I labeled 220 in the diagram because that's a standard value and it's pretty much the same, I just used the two 470s because I didn't have a 220 at hand.
Those values don't require much precision, since the main use of those resistors is to pull-down the input (that's the 100k) and to limit a bit the current from the RPi (that's the 220). The 220 can affect though, as the transistor's gain will also be affected by it, so it can't be too big. You can safely use 1/8W resistors for these.
The one that really affects performance is the 3.3 ohms, as they will determine the current going through the solenoid.
I say 4.3V since there's 5V from the supply and when the transistor is "on", there's roughly 0.7V that fall there.
The diode is quite important: the solenoid is basically a coil, and coils don't like to be abruptly interrupted when they have a current :P so the diode allows the circuit not to explode when the transistor goes to "off" (what would probably happen otherwise is that a voltage peak would burn the transistor).
Hi Matt, that's great news!
It might work with 5V, but the thing to worry about is current. I think the best thing to do would be to measure the current going through the solenoid (you could connect the multimeter in series with it), to make sure it's not too high for the driver circuit. Or you could do it the hardcore way - connecting the driver and checking how long you can keep it on until it blows up :)
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