TY, and good eye, I will replace with a mosfet, the multi-vibrator only runs on 11mA, so I am confident that it will be ok, although I did notice on a quick test it takes a few pulses to "ring up". Also I also wonder if low battery voltage could cause problem with frequency here, and whats a good fix.?
And! I just noticed that the IR LED is powered by RC5 too, so i will fix that and move that node to the 5v rail, even though i believe the port can handle up to 500mA.
I did think about direct oscillation to IR from pic, but decided to go with hardware driver and use the pic for other processes... although maybe it would be a good idea to replace multi-vibrator with another second micro-controller?
A huge question that is dawning on me though is about the solar and battery circuit. my calculation is that on a 1/2 watt@5volt panel i will get about 100mA out of it.
the driver is 55 mA, the RG&B LEDs are about 60ma, the IR LED another 20ma or so... plus another mA or so for the PIC and R7 + R8.... which totals 136mA. So i will need 12 hrs (of full light) charge time for 8hrs of run time(at full brightness), does that sound right? maybe it would help to increase the values of R1&R4 to 10k too?
Also with a 5v panel plus a diode, charging 3 series batteries to 4.5v may not be ideal.... but only 2 batteries is 3v@full charge and may not be enough to illuminate the LEDs ... any thoughts on how to handle this?
also what is a good IR LED to use for this, I am splitting the IR beam in to 4 and i would like to have a range of 1 or 2 meters per beam?
forgot to add parts list, I will add it to original post to-nite....
All very valid concerns. You will definitely want to shave off as much current as possible to give it the longest run time even if light conditions are not ideal.
A multivibrator definitely will take a few cycles to reach full amplitude. I don't know if that is an issue for your application or not. The frequency of the oscillation is mostly based on the phase shift of the two RC delay circuits, so it should be relatively frequncy stable vs. supply voltage, but it may eventually be affected if the voltage starts to get very low. It probably wouldn't be too hard to test the multivibrator on a variable power supply to see if the frequency starts to change or just cuts out entirely below a certain voltage, keeping in mind that the IO pin of the PIC may not output at the full supply rail voltage for the full circuit
At 40kHz with a relatively low input capacitance FET like a 2n7000, it should be no issue to raise R1 and R4 to 10k, although you'll probably also want to adjust R2, R3, and C1-4 accordingly. For a 2n7000 with a 60pF input capacitance, I estimate that you could probably go as high as about 22K or so on your collector resistors before you started to see third harmonic rolloff on your square wave due to the input capacitance. Those multivibrators don't really give a very sharp square wave to begin with, though.
Certainly with the increased resistance for R1 and R4, the current draw will be pretty minimal, so if you need the multivibrator to be "instant-on", you could try just running the multivibrator all the time directly from the supply rail and instead connecting RC5 to R5 so that the IR LED will only light when RC5 is high, even though the square wave vibrator is still running.
By the way, what are the functions of D3 and D2? Actually, um... what is the function of the circuit as a whole? Maybe I missed something, but I haven't actually worked out what the circuit does...
Also, for 3 batteries in series, 4.5V shouldn't be a major issue. I'm assuming that you are using NiMH-type rechargeable cells? You could always try a 4.2V lithium cell, but then you have to deal with the issue of charge regulation and protection on the cell.