Thread: Discussion MJX-F45 Single Rotor FP
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Old Jan 11, 2013, 06:58 AM
tiggertoo1962 is offline
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Originally Posted by BobTopofTheWorld View Post
All this talk of undervoltage indicators got me thinking... whats all the fuss over, we are talking like 6-7 parts, only 1 is a 'centipede' and the rest can be built on the IC. Is adjustable and will drive a LED AND a piezo 'annoyance device'.
Ok for the specifics:
LM 741 op amp (8 pin dip plastic case is best)
100,000 ohm mini potentiometer
27k 1/2 watt resistor
few assorted resistors from 500 ohm to 2.2 k 1/2 watt (to dial in the piezo)
5.1 volt 1/2 watt zener diode (anything from 4.2 to 5.1 volt will work)
Piezoelectric beeper (micro is good)

Following the diagram, it is a quite simple task to build it right between the legs of the centipede. The IC is tough so dont worry too much about static (MOS devices are REAL static sensative, this isnt one of them). As to the piezo, it attaches to the + rail and to pin 6 of the IC through the 500 or so ohm resistor (selected by you for best beeper annoyance) and can straddle the IC too.
OK to calibrate the beastie: with a reliable voltmeter connected, discharge a battery (or connect a calibrated source) to the point you wish to be warned, 6.4 volts as I recall (3.2 v per cell) and carefully adjust the 100k pot until it yelps/lights the led. Lower the discharge rate (raising the voltage) and verify the alarm stops, and again raise discharge to lower the voltage to alarm level, fine tuning as reqd. As this is a simple comparator, once set properly it wont require resetting (unless you change the battery voltage).
After it is set properly, one can simply cover the whole ic with a suitable glob of silicon sealant, or mount on a suitable insulated non-metalic surface as desired. Of course dont fill the piezo's output 'hole' with silicone, that kinda defeats its purpose.
I believe the monitoring of a single cell in a multiple cell battery is ignorant. What if the cell thats not monitor'd decides to droop? The 3.2 v warning device WONT DO YOU ANY GOOD in such a situation (and I bet its nawt long before we hear about it). Set up the alarm to read the full voltage, then if any one cell gets grumpy , the alarm circuit will act as intended.
Let me know if you lot like my style, I got plenty of ideas, and it has been a long time since I taught univ level electronics.
Cheers lads
Originally Posted by rexless View Post
I don't know nearly enough about electronics to understand how that works but I could probably assemble from your diagram if I knew where to buy parts.
rexless, I'll take this one up (or down ) a level...

Bob!! You're the very man I've been looking for!!

Think you could explain to me why the electricity doesn't fall out of the wall socket when I pull the plug??

Only HALF kidding . Give me something mechanical in my hands and a bit of time, and I've a fair chance of figuring out how it works. Give me something electrical, and you'd better give me an electrician along with it .
My dad was a spark to trade, but I reckon all that rubbed off on me was the static .
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