[time-nuts] help

[Adrian Godwin]

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 <jimlux at 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 at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>