I think this will work but I would like a pro's view on this.
I am using a Omron latching relay with the Arduino to conserve power when the relay is SET. Basically I will connect 2 Digi pins to the coil, keeping both HIGH. to SET the relay I will pulse pin 13 LOW, then to RESET the relay I will pulse pin 12 LOW.
Here is my issue, I want to use a manual switch to "reset" the relay manually.
Here is my theory, R1 is about 3 times the coil resistance of the relay, so when the switch is pressed it should pull the SET side of the relay LOW so it resets. Both pins 13 and 12 will be HIGH at the time so it will also pull pin 12 LOW, R1 should limit the current drawn on pin 12 long enough to protect the pin from a short. I am also thinking of adding a PTC in case the switch gets pressed for a long duration, it should then heat up and trip.
Whats your take? Ok or is there better way to do it?
Here is my theory, R1 is about 3 times the coil resistance of the relay, so when the switch is pressed it should pull the SET side of the relay LOW so it resets. Both pins 13 and 12 will be HIGH at the time so it will also pull pin 12 LOW, R1 should limit the current drawn on pin 12 long enough to protect the pin from a short. I am also thinking of adding a PTC in case the switch gets pressed for a long duration, it should then heat up and trip.
Whats your take? Ok or is there better way to do it?
Thanks
Well putting off the manual switch for the moment, the fact that it is a 5vdc coil relay and you have now added a 470 ohm resistor in series, there not be enough series current for the relay to even work, setting or resetting as the majority of the voltage will be dropped across the resistor.
Also I'm pretty sure you won't find a PTC rated for the 40ma max pin current recommendation.
the fact that it is a 5vdc coil relay and you have now added a 470 ohm resistor in series, there not be enough series current for the relay to even work,
Correct, about as High I can go is 120ohm for reliable operation,
Mouser listed one in the search, but after checking the data sheet it is actually a 0.05 hold and trip @ 0.12
Thanks, any other suggestions?
Maybe a 3v relay? Then I could use a larger resistor. EDIT
Well maybe not, after looking at lower voltage relays, they all pull more current than the 5v relay, so the trade off isn't that great.
Don't know how useful this might be to you but here is a circuit I used to allow a picaxe 08M micro to perform auto power off using a 5vdc single coil latching relay. Works great.
The trick with using the cap allowed me to only have to use one pin. After manually pushing the power on momentary switch the picaxe code would set the output pin high at startup setting the relay and 'sealing the power on switch contact, and when the program wanted to power off, it just sets the output pin low. Plus you save an output pin and no continous current drain using the relay. I love latching relays.
The cap serves two functions, to store a charge so the low going output pin would reset the relay and being a cap no continous current flows so no battery current drained by the coil. I had to play some to get the correct value of cap and resistor to function reliably, but after that it works great. I bought 10 of these relays for $5 on E-bay some time ago.
EDIT: I think my design would do what you want, having a manually switched way to reset the relay. If you wire a SPDT manual switch with the common going to the top relay coil, the normall closed contact to the output pin and the normally open contact to ground. The output pin would be free to set or reset the relay by going high or low, but once high you would be free to activate the manual switch to reset the coil.
