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Author Topic: Want to build a low power sensor but have not the faintest idea(can follow diag)  (Read 2322 times)

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Hi There everyone! I have a simple requirement. However the components must be cheap. I am after a simple sensor to run an LED lighting array (3 LEDs), the sensor must detect a dense dark object put in front of it and in turn switch on a 3 LEDs. The object will be no more than about 100- 60mm or less, in front of the sensor. However the power supply will be limited to one, possibly 2 9v D cells. The LEDs must stay on once activated and switch off when the item is removed. The LEDs must sustain for days not hours on the available power. Can you help. All options considered eg power supply with rechargeable batteries but I ahve bo idea again about charge controllers. Warmest Regards Steve


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You can simply put a mechanical switch so when you place the object it pushes the switch. This is the simplest and most efficient method, id draws literally no quiescence or operating current at all.
Other method is to make a light beam pair. You put an LED to emit a narrow beam of light to a photocell. When the object is placed between the LED nd the photocell, a relay is activated. You can use this circuit:
Light / Dark Activated Relay