Re: [tracker2] Re: how to beacon one last time.
- Occam's razor applies. Use the simplest solution.
As a young engineer, my chief engineer asked me to design a system to give a secondary request-to-send pulse for 300 mS over a com line to trigger a cash register tape to rewind and send its data.
I used a crystal oscillator, and a count-down set of flip-flops, to arrive at the 300 mS, Heath Robinson (Rube Goldberg for you Americans) would have been proud of my effort. I proudly showed it to the chief engineer and he laughed, replacing it with a simple RC network.
Nowadays we have supercaps, I would go with the idea of using one to keep the radio and tracker up for one last beacon.
On 15/06/11 19:08, Wes Johnston, AI4PX wrote:
I had drawn up a circuit that used two 555 timers, 1 fires 5 minutes after shutdown, the other fires one second after that to break a latched relay. It just got to a point where the parts count and complexity was/is just too high. It could easily be done with a small pic processor clocked at 32khz or so.... I do like the idea of a relay staying on until PTT gets asserted one last time.
but, since the ATV is confined to the area right around my house, I decided it would just be easier to set it at a fixed beacon rate of once a minute and a minimal path and the timer can then be a RC network on the base of a darlington pair that drives the relay. Moderately sized eletrolytics can hold that up for 3 or 4 minutes before releasing the relay.
The world needs more geniuses with humility because there are so few of us left.
On Wed, Jun 15, 2011 at 18:16, ac2ev <ac2ev@...> wrote:
What about a "Super capacitor" or small secondary power source that can survive a full discharge? You would want to size it so that it could power the radio for a short time before it is discharged. Then when the ATV is started back up it would charge again.
8< snip--- In firstname.lastname@example.org, "Wes Johnston, AI4PX" <johnstonwes@...> wrote:
> I have an ATV that I only use on the weekends sometimes not for 2 or 3 weeks
> at a time. I'd like to put a tracker on it that has absolutely 0 current
> draw when off. Yes, I know I could program the T2 to not transmit if the
> voltage is below 13.0, but it still has to draw power to check the battery.
> What I'd like to do is have it automatically come on and after the ATV is
> parked tx one last time and go to a zero power state.
> To this end, I've thought about a latched relay that gets interupted by the
> PTT, but it would just stay on until the moment PTT was asserted and turn
> off just as the packet started to tx. Probably the best solution is to have
> a relay unlatch on the rising edge of PTT.
> I've also thought about putting the GPS on switched power (ignition switch)
> and the T2 tied to the battery and just telling it to not tx on no fix....
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