Hi,
I'm trying to switch a relay with a fio (3.3v), the relay can be switched with 3v, this is the relay http://www.tme.eu/en/Document/321c4bbe0ad51b71622dddbb557c185b/G5V1.pdf
For testing i just connect one side of the coil to arduino gnd and the other side to digital pin 5.
This is the sketch i run in the fio
void setup() {
pinMode(5, OUTPUT);
digitalWrite(5,HIGH);
}
for some reason the relay is not switching. If instead of pin 5 i connect the coil to the fio 3.3v pin it is switched ok
So outputing 3.3v 40ma from digital pin 5 is not working, but outputing 3.3v 40ma from the 3.3v pin works...
I dont understand what is wrong.
Output pin is overloaded (50mA) and voltage drops.
Try two outputpins at once with bitbanging. !!! be sure NOT miss something when doing so - it may kill fio.
(so does driving that coil from one output)
I seriously doubt that the pin can provide 40mA at 3.3V, unless we are talking about short circuit current.
Powered at 3.3V with a load of 15-20mA the output drops right away to 2V, so you'll have to use a transistor
Then, of course, there are ethical issues about powering a relay from a uC, even with a diode.
The inductive load at switch off can, in the best scenario, reset your device.
You could either modify your circuit or use something like this:
http://www.ebay.co.uk/itm/1-Channel-5V-Relay-Module-Shield-Board-f-Arduino-ARM-PIC-AVR-DSP-ARM-Electronic-/201084471345?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2ed1918831
Which can be powered from a 5V supply BEFORE the arduino regulator (in order to clean any voltage spikes).
This one can work with a 3.3V trigger signal, while powered by a 5V supply, since its driven by the transistor, so the load to the arduino will be, at most, 1mA
I shall remember that using a transistor you need to power it up from the 5V line as well(Only the command will be triggered at 3.3V) A typical transistor has a VCESAT of 0.5 to 0.7V, so if powered from the 3.3V line the relay will only see 2.5 to 2.8V