Jaldi Labs

Aa Jao!

Solar power comes to JaldiLabs

Heh.  Sorta.

Setup a circuit to supplement battery power on the TMP36 temperature sender. Unfortunately, I have a long way to go before I fully understand what I’m dealing with here.

  • Transistors are not just trivial on/off logic switches.
  • I’m trying to use a 2.2 V supply (from the solar cell array) to switch a 3 V supply (from the battery).
  • Solar cells do not behave trivially, either.

Here’s a picture of the working breadboard configuration:


Here’s the power part of the circuit – feeds a 3.3 V boost regulator that powers the TMP36 and XBee. The diagram is from iCircuit.


I’m certain that there are issues with this circuit that I don’t get yet. (It’s ok – that’s why you do this, to discover what you don’t know.)

The idea was that if the solar panel is supplying power, it shuts off power from the battery, and if the solar panel is not supplying power, the battery powers the circuit. The battery is not rechargeable, just a couple of typical AA’s.

The circuit works, at least in the limiting cases.

Main issue right now is the intermediate case, where PV output is somewhere between fully on and fully off, and transistor stuff I have by no means fully understood comes into play. More to come.

XBee signal strength

OK, this is the raw value of rssi, small is good, big is bad.  The signal fails after a value of 85 or so.

The numbers are hex values that convert to -dBm, but I need to fully understand this before I do a proper conversion and/or interpretation.

For reference, on 6.21.12, the transmitter and receiver XBee’s are about 4 feet apart through a double-paned window and metal/concrete surround. The signal strength is reading about 68.

The lowest rssi value I’ve seen on my desk was about 32.

Where things are

The receiver XBee is sitting on a MacMini in a corner, behind the lovely jasmine:

The transmitter is only about 15 feet away, outside, enclosed in a plastic container and a ziploc bag, held in place by a soapstone rhino that has seen its share of Chicago winters:

The range on this setup is terrible. Nowhere near the ‘300 feet’ range that some literature suggests for the Series 1 – my signal is dropping to borderline if I move the transmitter 20 feet farther out onto our terrace. Don’t know what the problem is yet…

Maybe I’ll add the signal strength to the Cosm feed.