They're a LED and some current limiting. Some are specced as low as 3V and 10mA but they're optimised for 12-24. I'd definitely use a transistor and at least 5V, especially from something like a Pi or Teensy, which have 3v3 logic levels.
My reading is that Bill doesn't want to mess around with micros and electronics, though. He wants an off-the-shelf timeswitch that - for perfectly understandable reasons of engineering pedantry - is always correct. On Mon, May 2, 2016 at 5:56 PM, jimlux <jim...@earthlink.net> wrote: > On 5/2/16 8:24 AM, Nick Sayer via time-nuts wrote: > >> To flesh this out a bit more, on a Raspberry Pi, it would be easy to make >> a cron job that would pulse a GPIO pin high. They really *want* you to use >> Python (thus the name), but this is easy to do in just a shell script. >> First, do this to set things up: >> >> #! /bin/sh >> >> GPIO_PIN=9 # pick whatever one you like >> >> echo $GPIO_PIN > /sys/class/gpio/export >> echo out > /sys/class/gpio/gpio${GPIO_PIN}/direction >> echo 0 > /sys/class/gpio/gpio${GPIO_PIN}/value >> >> Next, run this script out of cron: >> >> #! /bin/sh >> >> GPIO_PIN=9 >> echo 1 > /sys/class/gpio/gpio${GPIO_PIN}/value >> sleep 1 >> echo 0 > /sys/class/gpio/gpio${GPIO_PIN}/value >> >> That will make a positive going pulse with the leading edge synchronized >> to cron (for sufficiently vague definitions of “synchronized”). >> >> As for the hardware side, take the GPIO pin and connect a 10k resistor >> between it and the base of a 2N4401 transistor. Connect the emitter to >> ground and the collector is a classic “open collector” switching output. >> Think of it like a switch connection to ground. When it’s on, there is a >> low impedance path to ground. When it’s off, it’s high impedance. You can >> use it to work a relay (be sure to add a flyback diode across the relay >> coil) or directly to switch any load that doesn’t exceed the abilities of >> the transistor. >> >> If you want to be a little safer, you can use an opto-isolator instead. >> Connect the GPIO pin to a 150 Ω resistor and then to the anode of the LED >> in an optoisolator. Connect the cathode to ground. The optoisolator itself >> can be either a phototransistor type or a driver triac type (the latter >> would be used to drive a power triac to switch AC loads on and off). >> >> >> > > SSR data sheet at mouser (they are <$20) > http://www.mouser.com/ds/2/307/g3na_ds_e_11_1_csm165-892371.pdf > > myriad varieties of inputs and outputs, whether it has an indicator (nice > for testing), whether it's a zero voltage switch. > > BUT.. it kind of looks like it wants to see 4V to turn on for sure. Maybe > your 5V USB powered widget puts out that on a GPIO pin, maybe it doesn't. > I've had very mixed luck with driving SSRs directly from logic (because the > real threshold voltage and the real logic output voltage vary with > temperature, for instance). > > I'd use the extra transistor as an open collector and a 12V wall wart or > similar to provide the current for the SSR input. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.