9V Battery Low Voltage Monitor
First, I'd like to give thanks and credit to Dave Johnson at http://www.discovercircuits.com for all the help. He provided the final circuit design which is available below. I had a working 741 op amp circuit
that required a seperate 9V battery and it had some flaws in the design and implementation.
Mr.Johnson was generous with advice and tips which pointed me in the right direction. I simply
built the circuit he provided.
This circuit is designed to monitor the voltage in a 9V system. When the voltage drops to 7.2V
the indicator led will light up. The best thing about it is that it runs on a single 9V supply (the V2's 6 D Cells) and can
be connected directly to the Robosapien V2's power switch leads. I did it this way so it would all be attached to the back
body plate.
The LTC1440 Low Power Comparator IC is available at Digi-Key. I ordered it online. It
conumes only 4 micro-amps as opposed the the milli-amps my circuit was consuming. I used an IC socket to keep the IC from
taking heat while soldering. I used resistors I had already had, added in series to make up the resistances needed for the
voltage divider. That is why there are so many on the board.
Threshold Voltage = 1.18 * ((R1 + R2) / R2)
Here are some various trip points whether
using a 9V or 7.2V Supply. These should be accurate. I have not tested them as my circuit is hardwired now and would have
to take my V2 apart again to do it.
Just use R2 at the listed resistance to get the listed trip point:
The 9V Battery Monitor with a fresh battery.
The 9V Battery Monitor with a depleted battery.
A blurry close up of the perf board circuit.
The battery monitor in the V2 with fresh batteries.
The battery monitor in the V2 with depleted batteries. (Hard to see, but the LED is lit. I could not get a "toned
down" picture of the LED lit.)
First hack/add on by feedback.
Feel free to e-mail me here.
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