Mimimize power consumption of circuit

[Microshan]

Hi all,
I have been building a capacitive soil moisture probe using the circuit shown below.
The circuit works reasonably in this 1^st test version, but it uses way too much power/current in standby mode to be operated by a 9V battery.



The workings of the circuit are quite straight forward. IC1A & B forms an oscillator. The output is fed to a voltage divider consisting of C3(C4) and the probe. The signal is rectified and amplified and fed to an other low frequency oscillator driving the Led.

In the current configuration and used components it uses around 3mA.
How can I, without doing the whole circuit over, reduce the power consumption of this circuit to be useful for battery use.

Kind regards
Mike

[audioguru]

A 9V battery has tiny little low capacity AAAA cells inside.
Use three or four AA or AAA cells for much longer battery life.

[Hero999]

Four rechargeable AA cells in series should last over 800 hours with the circuit as you've drawn it.

If you want to reduce the power consumption further, then use a micropower op-amp such as the OP290.

[Microshan]

Thanks guys,

I'll try to replace the LM358 with a OP290. They seem to be pin compatible. But I'll try a simulation first.
The reason for choosing a 9V was a purely for space reasons. Might be able to lower the supply to 6V. More simulation I guess :)

Mike

[Hero999]

If you used the 74HC132 (note the different pin-out), as well as the OP290, the whole circuit will work down to 2V, enabling you to be able to run it from two AA cells.

[Microshan]

Thanks for the reply,

I'll try the suggested changes. Unfortunatly I only have access to my local electonics shop in the week-ends so experimenting will continue in the week-end.
The good thing - it gives me some time to redo the circuit board.

Regards,
Mike