This is a simple, cheap and low power sensor which can be used, for example, with your favorite battery powered node, for counting power meters blinking led pulses.
I've decided to not use the well known LM393 module with photodiode because the combo has some power consumption (0.4mA for the comparator only + rest of the circuit, even if no pulses).
I also thought there is not always the possibility to have an external power supply, when power counters are outdoor for instance. But sure, the advantage to use a comparator is we get a nice digital voltage level for the signal to the node.
So I got the idea to use a mosfet with a photoresistor and just a few resistors, which i think should be enough :)
Lot of docs about photoresistors on the internet, but quickly, the photoresistor operation is very simple, and allow us to be low power though:
And i've used it like this :
I've quickly tested it with a signal generator and was able to detect up to 100Hz. Which should be enough for lot of power meters i think.. An example, for 50Hz frequency blinking led :
I've done two pcb versions that you can order here in case you want to play with it:
An SMD Jumper is also available. Shunt it by soldering, if you need the led indicator (will use a bit more power, tweak the resistor|
To use the board, that's easy:
I don't really need it, or maybe in future, because where I live there are others alternatives like a grid protocol providing lots of informations, but that was quick and fun to do!
Copyright Scalz (2016). released under the CERN Open Hardware Licence v1.2
|Qty||Value||Device||Package||Parts||Description||MF||MPN||Aliexpress or Ebay link|
|1||330||RES||R1,R3||Through-hole or 0603|
|1||100||RES||R2||Through-hole or 0603|
|1||1k5||RES||R4||Through-hole or 0603|
|1||LED||LED1||For through hole 5mm, for SMD 0805|
|1||P-Mosfet||Q1||BS250 like, or CJ2305 SOT23-3etc.. for SMD|
|1||NSL-19M51||PHOTORES||TO18||LDR1||Photoresistor NSL-19M51 type|