[time-nuts] help

Adrian Godwin artgodwin at gmail.com
Mon May 2 18:32:17 UTC 2016


Here's a possible solution. It's ethernet-connected and will switch a 10A
output. It's made for UK use but would probably be fine if you have a 220V
supply. It doesn't say whether it tracks NTP, but looking at the specs i'd
suggest it's linux inside and can do that.

http://www.audon.co.uk/webcontrol/EZ-21g.html


On Mon, May 2, 2016 at 7:21 PM, Adrian Godwin <artgodwin at gmail.com> wrote:

> 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.
>>
>>
>>
>>
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>
>



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