Not sure what your thinking is here. This unit is never hooked up to anything more exotic than a speaker microphone which is just an 8 ohm speaker which may or may not have some frequency shaping going on in its enclosure. All testing was done with a speaker mic or a bare 8 ohm speaker. Altering every speaker mic that gets hooked up to this puppy is not practical (or a good idea on the submergible microphones) so that's not an option. I'm not able to get a cap close to the speaker.
One of the reasons for using a BTL chip is to get rid of the coupling caps. This latest version added conditioned power, polarity protection, new negative rail, additional filter section, logic controlled transmitter selector and 6 new wire to board connectors. It all had to fit in the original enclosure so eliminating the 'relatively' large output cap made a great deal of room on the board.
I'm satisfied the chip is performing well for it's intended application. I could get better battery life I'm sure but total draw is 33mA (most of which comes from the pwr on LED). I expect about 18 hours on a 9 volt. Future plans include a larger (shielded) enclosure, rechargeable AA battery pack plus a micro controller to PWM the LED and provide audible and visible function alerts to the user. Initial estimates place battery life at 60 hours with these mods.
I'd like to go to a chip amp that has a shutdown mode but I'm not sure how to apply it here or if that would actually accomplish much with a system monitoring active radio traffic. Would it ever shutdown?
De-rating a normal 20ma led for long life, has it running 8ma or less.
PWM (ac) is so you don't have a 1.7v ordinary led waste 3.3v (and current by same proportion) into a resistor (that whole PWM circuit is for replacing a resistor). However, there's other ways to use LED's that won't need the PWM circuit.
For greater simplicity, send extra electricity into additional LED's instead of wasting current into a high value resistor. An easy option with just one LED is to select a more efficient very high brightness 3v LED and then decrease current. Or, a series pair of high brightness clear-body orange or yellow would come up to slightly over 4v (simply add an ordinary diode to raise that to ~4.7V and then a token resistor, and you'll have a battery level indication too). Pair of 2v led's takes even less space than one LED plus a PWM circuit. 🙂
A painted/colored bodied LED is quite dim in appearance; however, a clear bodied 5mm flat top LED can be quite bright looking and still manage to work from a wide angle.
PWM (ac) is so you don't have a 1.7v ordinary led waste 3.3v (and current by same proportion) into a resistor (that whole PWM circuit is for replacing a resistor). However, there's other ways to use LED's that won't need the PWM circuit.
For greater simplicity, send extra electricity into additional LED's instead of wasting current into a high value resistor. An easy option with just one LED is to select a more efficient very high brightness 3v LED and then decrease current. Or, a series pair of high brightness clear-body orange or yellow would come up to slightly over 4v (simply add an ordinary diode to raise that to ~4.7V and then a token resistor, and you'll have a battery level indication too). Pair of 2v led's takes even less space than one LED plus a PWM circuit. 🙂
A painted/colored bodied LED is quite dim in appearance; however, a clear bodied 5mm flat top LED can be quite bright looking and still manage to work from a wide angle.
Yeah that would work however the idea behind the microcontroller is to allow more control over the LED and for other operations on the board.. A pwr indicator doesn't need to be on constantly. I would have it lit for 10 seconds on startup then pulse once every 2 seconds after that. Much more efficient I would think. I also intend to add other functions to the circuit such as audible alerts for important switch positions, batt low, alert cancel and some other control operations now done with dedicated IC's. Project creep in action.
Well, I think it is very smart that you inspected other proposals before coming up with all of the answers on your own, and you did. A broader range of possibilities is almost always a good thing except takes a little more time; but, the benefit is that likelihood of a do-over is decreased. So, kudos for that!
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