the ioio board puts 3.3v 20ma out on a pin when high and I need to power the 3v 130mA relay with it, the ioio board itself is powered by usb 5v.Welcome to AAC!
You will need a transistor to drive the relay. What is your 3V supply; battery (what type?) or wall-wart?
Here's how you could do it:-
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I missed that part about automobile modification in tos I cant seem to edit my post to remove that sentence im not actually modifying automobile per se but sorry for that sentence just the same. And thank you for the awesome tip.Well in my circuit above, just replace the 3V source with 5V and add a 15 Ohm 1W resistor in series with the relay coil.
I do not recommend this for automobile use; that would be contrary to the Terms of Service of this site.
3 more questions im looking at radio shack they have the following which is better for my need ?Well in my circuit above, just replace the 3V source with 5V and add a 15 Ohm 1W resistor in series with the relay coil.
so replace 2n3391a with 2N7000?Also look at the fet designed for that application in mind, the 2n7000.
Does not impose any load on the source.
Max.
I saw mention of the 5 volts being from a USB port. You may want to give this a read. While over the years the USB port has evolved and can deliver more current than years ago, it is not a source of unlimited current, even today. So for example if I have 5 relay coils driven by the USB port and each coil draws 130mA then 5 * .130 Amp = 0.650 Amp if all coils are energized at the same time. Just something to keep in mind.and last question is i need to put about 5 of these circuits on a board would that be an issue using the same supply and ground for them all or should i do something differently? i have some spare 7805 regulators from radio shack could I use them to supply the 5v directly from the 12v supply ?
I was thinking about that, the board itself is currently powered from usb but i was thinking about using the 7805's and getting off the usb or leaving the board on the usb but using the 7805's for the relay/coil circuits. maybe 1 7805 for the circuit and 1 for the board? I really appreciate the info and helpDon't know as this will matter or not but where you mention:
I saw mention of the 5 volts being from a USB port. You may want to give this a read. While over the years the USB port has evolved and can deliver more current than years ago, it is not a source of unlimited current, even today. So for example if I have 5 relay coils driven by the USB port and each coil draws 130mA then 5 * .130 Amp = 0.650 Amp if all coils are energized at the same time. Just something to keep in mind.
I would also consider the 2N7000 series which Max has me sold on.
Ron
That is what I would do, unless of course you are already sitting on a pile of relays with 3 volt coils.I'd just get a 5V regulated power supply (not 12V) and use 5V relays via the same transistor driver above
No need for 3V relays.. its just more parts/wasted heat.
That was my assumption when suggesting a resistor in series with the relay coil (and I see no relays in the post #7 shopping list). 5V relays would be better if a 7805 is used; or even use 12V relays and ditch the 7805.unless of course you are already sitting on a pile of relays with 3 volt coils
Looking at the specs of the IOIO it seems to accept up to 10V on the Vin pin so thats why I said 5V..That was my assumption when suggesting a resistor in series with the relay coil (and I see no relays in the post #7 shopping list). 5V relays would be better if a 7805 is used; or even use 12V relays and ditch the 7805.
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