Tuesday, October 26, 2010

SGP4 on PIC32 Observations

Because I'd like to move to the SGP4 tracking algorithm for QRPtracker (and failed to port it well to the 8-bit ATMega644) and because there's no substitute for real programming power, I'm playing around with the PIC32 processor, as conveniently provided in the CUI32 experimenter's board. My goal is to milk this for all its SRAM and flash, but keep the power down to the single-digit mA level so that I can use a pair of AA batteries to power it.

Here's some power observations to get things going:

ProgramSpeedOtherPower (mA)
Switch80MHzBoth leds on75
Only red led on72.7
'Picdict'Waiting input57.7
Running calculations60.0
7.5MHzWaiting input21.7
Running calculations13.5

('Switch' is a program that just continually makes the state of the green led equal to that of a push-button. 'Picdict' uses the on-board realtime clock to calculate the state vectors of satellites and to determine their az/els from a given ground station.)

I think this is pretty good news. The red led, which is always on, probably uses about 2.3mA, and the net power consumption for the 7.5MHz clock running predict-style is 11.2mA with no other power-saving going on. We can put this to sleep for most of the time, dropping into the microA level. If during the brief necessary bursts, we are up in the low 10s of mA, I think it will be ok.

Of course, assuming that the processor is going to spend the vast majority of its time in idle, the real question is how low we can go with sleep and idle modes. Other power concerns are the LCD display and optional GPS engine, but the MCU was my concern.

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