Power Supplies

Over the past few nights, I've started testing some of the components on a breadboard. The Muscle Sensor v3 requires a positive and negative power supply. I could use two 9V batteries, but that would make the device bulkier. Also, the 500 mAh capacity of a 9V probably wouldn't last more than one night. Ideally, I'd like to run the whole project off of one, rechargeable lithium polymer battery.

I started researching dual power supplies and discovered a DC converter chip from Intersil, called the ICL7660. This magic little chip, along with a few capacitors, will create a dual supply up to 12V. What I didn't glean from the datasheet, but later discovered, is that the chip is only able to source a few milliamps before the voltage out starts to drop. With the Muscle Sensor connected and drawing about 15 mA, the output of the negative supply went from -4.18V to -3.7V.  A little more web searching turned up a similar chip from Analog Devices, the ADM660. It is rated for 100 mA of output current. The voltage dropoff charts also look much better. I'm going to order a few and give it a try.

After I stalled on the power supply, I starting preparing some of the other components. I soldered headers on to all of the breakout boards and got the accelerometer working in a few minutes with the sample code from SparkFun Electronics. Next task is the microSD card adapter.


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