I have progress! Catching up on 30+ years of electronics evolution, I discovered that the 555 timer chip can be wired in monostable mode, also called "one- shot" mode. In this mode it can be activated by a momentary pushbutton, upon which it activates an output pin, said pin stays high for a time period derived by changing values of two components, a capacitor (C) and a resistor (R), at expiration of time the pin goes low again.
The timing delay is calculated with T(secs) = 1.1 x R x C where R is resistor in ohms and C is capacitor in farads. Apparently the 555 can reliably goes as low as 10 milliseconds for this timing cycle, and as high as many many hours, and wiring multiple circuits of this type in series can give you days and days, not that I need this, but I thought it was cool anyway. therefore a 22uf cap and a 10k resistor will give 1.1 x 10000 x 0.000022 = 220 milliseconds I have built such a circuit on a breadboard and am happy to say it works. I used a 22uf cap and a potentiometer resistor adjustable from 0 - 10k ohms. I connected the output of the 555 to a 12v LED, and can see the difference in length of flash when adjusting the pot, yay! This gives me 0 - 220 (approx) milliseconds of adjustable "on" time. This adjustability is critical with a homemade canon as different valves are going to vary on air flow, and I don't have a marker-engineering R&D department :) When you push the button, the output goes high and the timing cycle starts, milliseconds later (depending on where the pot is set) the led switches off (output goes low again). It matters not if you release the button before the end of the timing cycle or if you hold the button in, it is a one-shot circuit, to "fire" again you must release the button and then press it again. To accomplish the second part of my requirement (delay to allow reload) another similar circuit can easily be connected in series. The one-shot circuit diagram is all over the net, but I used the below one as a reference as it seemed to have more protection built in than other examples I looked at: http://www.circuitdb.com/circuits/id/107 (tis the one on the right, and I have my 10K pot in place of the 47K resistor shown in the diagram) here is a pic of the buggery box, not pretty even for a prototype but it works like a champ :) http://www.holnet.net/images/tank/20090821/555%20one%20shot%20timer%2001.JPG runs of 12vdc In practice the output pin will switch a small solid state relay, which will switch the air valve. Canon firing-range data will determine if I guessed the right values for my resistor and capacitor, but being adjustable up to 0.22 seconds I think it will be ok and if not it can be easily changed. Ben Electronic-Battlefield Warfare Regiment - Southern Tankers --~--~---------~--~----~------------~-------~--~----~ You are currently subscribed to the "R/C Tank Combat" group. To post a message, send email to [email protected] To unsubscribe, send email to [email protected] Visit the group at http://groups.google.com/group/rctankcombat -~----------~----~----~----~------~----~------~--~---
