This article is about a simple Turn ON in the Dark light made with TSL257 Light to Voltage Converter IC (Integrated Circuit) that you can purchase from Rocky Electronics (https://rockby.com.au).
You can see this highly sensitive IC working in this video:
If you check the RSL257 datasheets you will notice that this IC can work with only a 3 V power supply, with a maximum supply voltage of 5.5 V.
Do not connect to 6 V or you will burn this IC.
Also, the maximum output current is only 3.5 mA and the typical current is only 1.9 mA. Thus you might need to increase the output current with a PNP BJT (Bipolar Junction Transistor). Do not use MOSFETs because the minimum threshold gate voltage that could be above your 3 V supply voltage.
The output voltage is approximately proportional to light intensity. When the IC is exposed to bright light the output voltage is equal to supply voltage. Higher light intensity means higher voltage. Thus in the dark, the output is close to zero.
An alternative circuit is explained here:
https://hackaday.io/page/7000-turn-on-in-the-dark-light
Step 1: Make the Circuit
I made the circuit with nothing more than:- small piece of matrix board,
- 3 V AAA battery harness (two AA batteries),
- TSL257 IC,
- big 20 mA LED (you can use a bright LED),
- and insulated wires.
Top View:
Bottom View:
Step 2: Testing
Testing videos:
Front view:
Conclusion
This light to voltage response of this IC seems to be very linear. This is a second reason why you should not connect a MOSFET to the output of this IC. This IC can be used for a linear light control system that can compensate for room darkness.
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