Light to activate microcontroller, battery life

[mramos1]

I designed my light detector. It is an LDR and cap to a pin on a microcontroller. And a transistor to piezo to beep.. Thanks to Nigel's joystick tutorial.

Problem, battery last 5 days (9volt transistor type).

Any ideas on using the LDR, it drops to 1K when the light is at the level I want to detect. Can I use it and a resistor to an FET to power the microcontroller? Any other ideas.

I bought some AVR tiny11 chipd that draw less power, but my programmer will not program them (for some reason), so look for other ideas.

Thanks.

 

[Nigel Goodwin]

I designed my light detector. It is an LDR and cap to a pin on a microcontroller. And a transistor to piezo to beep.. Thanks to Nigel's joystick tutorial.

Problem, battery last 5 days (9volt transistor type).

First thing, don't use a 9V battery, they have a vary low power to size ratio, using AA batteries will last far longer.

Second, by using 9V you're instantly wasting 4/9th of the power in the regulator, dropping it down to 5V. Use three AA batteries to power it!.

Thirdly, (as I believe I mentioned previously?), don't take continuous readings, there's no need - put the PIC to sleep and have it wake up under control of the watchdog timer and run the test, then go back to sleep again. The WDT is rather limited, so it's usual to only test every so many WDT timeouts.

Fourthly, run at a lower clock speed, power consumption is directly proportional to clock speed.

Any ideas on using the LDR, it drops to 1K when the light is at the level I want to detect. Can I use it and a resistor to an FET to power the microcontroller? Any other ideas.

How would that help?.

I bought some AVR tiny11 chipd that draw less power, but my programmer will not program them (for some reason), so look for other ideas.

How much less does it draw?, a PIC in sleep draws almost nothing?, and doesn't draw much when running - I doubt the consumption is down to the PIC?.

Quick check in the datasheet, for a 16F628A typical running consumption at 4MHz is 668uA, at 32KHz only 38uA, and typical sleep current is only 0.2uA.