Electronics expertise needed- Low Voltage Shutdown Alarm

PM650 said:
If you foresee many electronics projects in the future, you may want to consider buying assortments of components instead of individually (resistors & capacitors).
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its fun for me and i understand electricity very well for someone who has little education in the small stuff like this- i dont know the specifics and how to draw properly, but i understand how things work. sometimes i wonder if i should have gone the whole college/engineer route, yet i just couldnt do a job where i sit around all day. im getting into VDV union work next year, which will be a nice new set of technology for me to play with.... and its nice because i never have to have a gym membership- they pay me hella good to run a shit-ton of very long patch cables everywhere:p
 
Ok, it might be a better idea to use a large cap, but the tollerance will be 15% at best and the stability over time isn't great. Probably easier to choose an upper limit for the resistor & calculate it that way as you said. 15uF & 10M is probably what I would go with.
 
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All I can say is 99.9% of my electronics knowledge is from hobby/repair work and I just graduated as an EE in April. The only thing you'll be missing wrt to an engineering degree is a line or two on your resume, which may or may not be significant for a particular job. Btw VDV?
 
PM650 said:
Edit: Perhaps I'm wrong on the above paragraph, since your circuit isn't equivalent to the datasheet one I'm looking at. However the op-amp will be latched indefinitely (following the first low voltage), so the whole circuit will not be able to return to its initial state regardless of how the 555 is set up.
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first off i highly appreciate the feedback. this is exactly how i learn best. my understanding is, the timer circuit i drew up is designed so that once the 555 timer is powered on, it starts the 'countdown'. it then of course trips and remains in that state until power is removed.

so i guess it is confusing, because what i need is a main-power kill switch... and just eliminate the reset switch by the zener diode towards the left hand side. an overall kill switch would then reset both the timer and the comparator. i DO want to reset this manually each time- i dont want the battery to regain enough residual current to turn the computer back on. this is more like a fail-safe then a controller...
 
PM650 said:
All I can say is 99.9% of my electronics knowledge is from hobby/repair work and I just graduated as an EE in April. The only thing you'll be missing wrt to an engineering degree is a line or two on your resume, which may or may not be significant for a particular job. Btw VDV?
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Voice Data Video.

last year i worked on the fighting illini football stadium in illinois. we ran the speaker/pa system, security cameras, tv's and card access throughout the stadium. it was quite an experience, there is a lot of expensive top-of-the-line audio gear that gets played with... like hanging $600 a piece ceiling speakers everywhere, and terminating 40 million cat5 connections :D
 
If you want it to latch off permanently (until manual reset), why do you need a timer? I was thinking you implemented this to automatically reset after 3 mins if the low voltage condition is not present. Perhaps you could just explain exactly what inputs you want & what you want to happen in the event of each possible condition to be present - I'm a bit confused here :confused:
 
krupted said:
Voice Data Video.

last year i worked on the fighting illini football stadium in illinois. we ran the speaker/pa system, security cameras, tv's and card access throughout the stadium. it was quite an experience, there is a lot of expensive top-of-the-line audio gear that gets played with... like hanging $600 a piece ceiling speakers everywhere, and terminating 40 million cat5 connections :D
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Possibly not my idea of fun, but I get some exercise doing automotive repair somewhat often. If someone ever asks you to replace a heater core in a Pontiac Grand Prix - don't. Your back will never forgive you :p
Although I am in the process of building a few HT amps, not too many people who can't appreciate some expensive audio equipment ;)
 
:D my dad is a mechanic whos refused to touch my cars ;). i have lost a lot of skin to the big 3. talk about poor engineering... yikes.

honestly i did have 'dummy' ways of permanently latching the relay after the few minutes- if i was smart i would buy an actual latching relay i think.

My goal is-

sit in truck with computer on (built a pc into my dash and jumpseat), and when the battery is drained to the point (tbd) of weak, an warning light will flash on the dash and after a couple minutes the pc will shutoff. it will shutoff saving enough battery power to still start the car. i know this will only leave me about 20min of runtime since i cant use the battery down past 12v or so, and this is probably far too much messing around for what i need, but im unemployed i need something to do. besides, my carpc is highly customized, everything is custom fabbed.

also, the M2-atx DC-DC power supply i have handles the startups and shutdowns, its just a dummy when it comes to battery power. it will run a 12v battery down to 5v and continue to work fine... continuing to ruin the battery (ive seen it!). better power supplies handle the low voltage situations with intelligence, i just need to add that feature to mine.
 
turns out they only had 2M pots, so actually ill have to use a 100uf cap to get about 3min (1.7M ohms). i was putting the decimal place in wrong, i knew it was something dumb. the tolerance can be lax, it really doesnt matter if it shuts off in 3min or 4... or 2...

nice thing about this 2M pot is it takes 15 turns to rotate it fully. this should give me some very good control i hope.
 
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PM650 said:
I was thinking you implemented this to automatically reset after 3 mins if the low voltage condition is not present.
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ive been thinking about this, and to save a long explination i want this without auto reset. i do need to do it myself, hard to explain because there are so many situations only freaks that have pc's in their cars understand:eek:
 
krupted said:
:D my dad is a mechanic whos refused to touch my cars ;). i have lost a lot of skin to the big 3. talk about poor engineering... yikes.

honestly i did have 'dummy' ways of permanently latching the relay after the few minutes- if i was smart i would buy an actual latching relay i think.

My goal is-

sit in truck with computer on (built a pc into my dash and jumpseat), and when the battery is drained to the point (tbd) of weak, an warning light will flash on the dash and after a couple minutes the pc will shutoff. it will shutoff saving enough battery power to still start the car. i know this will only leave me about 20min of runtime since i cant use the battery down past 12v or so, and this is probably far too much messing around for what i need, but im unemployed i need something to do. besides, my carpc is highly customized, everything is custom fabbed.

also, the M2-atx DC-DC power supply i have handles the startups and shutdowns, its just a dummy when it comes to battery power. it will run a 12v battery down to 5v and continue to work fine... continuing to ruin the battery (ive seen it!). better power supplies handle the low voltage situations with intelligence, i just need to add that feature to mine.
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So, at the first instance that it detects a low voltage, it begins the timer - which will not be reset by restored >12V. So the timer counts down and shuts down the PC after 3 mins, regardless of the voltage thereafter and can only be turned on by hitting the reset switch.

In this case, the circuit will work but it will need to be modified to continue the count regardless if the op-amp output is latched. I'm still trying to get my mind around how you have the 555 configured - with pins 6 (Threshold) & 2 (Trigger) connected together, you have an astable oscillator, which isn't a timer.

What I would probably do is use the timer config. in the datasheet & turn the latched output of the opamp into a pulse for the TRIG input with a series capacitor. The transistor already present would act just like the switch in the datasheet diagram - just put a capacitor in series with TRIG.

Edit: Actually I just noticed the sequential timer in the datasheet is doing just this - it turns the latched output of the preceding stage into a pulse with a 0.001u/33k RC setup, don't I feel smart now lol.
 
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PM650 said:
Edit: Actually I just noticed the sequential timer in the datasheet is doing just this - it turns the latched output of the preceding stage into a pulse with a 0.001u/33k RC setup, don't I feel smart now lol.
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see that's where your edumacation comes in, i wouldnt have been able to know that. if you havent noticed by now all im basically doing is heavy google searches on basic circuits of the functions i want, then putting them together like a puzzle. the key then is to ask smart people if it will work, its really a beautiful system:)

here is the datasheet for the chip i ordered.

http://www.rapidonline.com/netalogue/specs/82-0336e.pdf
 
All 555s are basically the same. The datasheet I was referring to above is my previously linked TI sheet, look at the sequential timer on the p15.
 
yeah sorry i have been now, i do see it much clearer. the problem with the datasheets for new guys is they dont explain what the terms mean, like 'one shot timer'. it seems easy but if you dont know its just confusing.

added the cap to pin 5, im pretty clear how everything works now. it will be a few days until i get the parts, god knows what ill keep adding until then.
 
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parts finally came. shipping was slow due to the chinese origin, but its not a big deal. for $50, you get a fair amount of extra parts
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ill be attempting this over the weekend probably...
 
spent 3 hours making it tonight. went to hook it up and POP i hear. relay immediately clicks on and the whole thing is junk. why? i put on all the transistors backward apparently... i can only hope thats all i did wrong. it was nice and small too, it would have been awesome. oh well, thats why i bought extra parts.
 
krupted said:
spent 3 hours making it tonight. went to hook it up and POP i hear. relay immediately clicks on and the whole thing is junk. why? i put on all the transistors backward apparently... i can only hope thats all i did wrong. it was nice and small too, it would have been awesome. oh well, thats why i bought extra parts.
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Bad news indeed, but hopefully you'll never forget to check or double-check the datasheets, I usually have them open as I'm installing parts to make sure. Breadboarding things never hurts either, if you have the time.
 
yeah and i just bought a new tablet pc, there is no reason for me to not have it next to me so i could double check everything. also i think ill space everything out more and just make the device a lot bigger. it will make it much easier to construct and i have the space so its not like i had a real reason to make it so compact.
 
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