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Random Nonsense / Geek Stuff All those random tech ramblings you can't fit anywhere else! |
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09-02-2005, 11:37 AM | #1 |
Cooling Savant
Join Date: Jun 2002
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I need help with a basic circuit
I'm a CompE/EE student, but I haven't gotten into actually making circuits yet. Anyways, for FSAE, I "volunteered" to make a circuit for the car. Basically when the circuit recieves a 12v signal, it starts a timed delay, at the end of the delay, power is cut to another device. I was trying to accomplish this with a 555 timer and a d-type latch, but it doesn't work in the simulation software I'm using. Any help would be appreciated. Oh, BTW, I can't use relays, and the timer needs to have a variable delay.
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09-02-2005, 03:36 PM | #2 |
Cooling Savant
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what is the maximum delay that you will need?
This will tell you how to set up the inputs. The input setup will tell you how to design your circuit.
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09-02-2005, 11:39 PM | #3 | |
Cooling Savant
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09-03-2005, 12:09 AM | #4 |
Cooling Savant
Join Date: Mar 2002
Location: FL
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how bout something like this?
Code:
________ C0------------->| | C1------------->| | C2------------->| | C3------------->| |---------->12v C4------------->| | C5------------->| | --------- ^ | | 12v the 6 control lines (C0-C5) allow you to make settings from 0 - 63 seconds (standard binary values). 12V input is constantly applied, and this go's through the circuit, which allowes it to pass through to the output for as long as the control lines are set higher than 000000. Once the timer reaches the value passed in through the control lines, the voltage is cut off to the output, and the control is reset to 000000. The circuitis then redy to accept a new control value, and start the cycle all over again Does this sound like it would work for your application? If so, we can start working on the circuitry to drive it.
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When you do things right, people won't be sure youv'e done anything at all. Looking to buy/trade for used Deep Fryer and Vacume Pack Sealer. |
09-03-2005, 01:11 AM | #5 | |
Cooling Savant
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There is no reason why your idea would not work, is it possible that it may not be working due to simulator setting? Just out of curiosity what sim are you using?
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09-06-2005, 06:54 PM | #6 |
Cooling Savant
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Superart, your idea would work but having the timer controlled with a potentiometer would be more useful for me. As for the simulation program, I'm using multisim.
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09-06-2005, 09:51 PM | #7 |
Cooling Savant
Join Date: Mar 2002
Location: FL
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How would you use a pot for this?
Say for example, you set the pot for 3 seconds.... The timer kicks in, and passes the 12V along for 3 seconds. After 3 seconds, the timer expires, but since the pot is analog, i is still set to 3 seconds, and the circuit is still set to read it. So instantly, when the timer expires, it is reset for 3 seconds. so, basicly, what you get is a constant on situation. Although I could be wrong. What does your sim say? Just out of cureosity, what is this circuit being used for, and what school do you go to?
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When you do things right, people won't be sure youv'e done anything at all. Looking to buy/trade for used Deep Fryer and Vacume Pack Sealer. |
09-07-2005, 06:21 PM | #8 |
Cooling Savant
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I go to UMR and the circuit provides an "idiot" function for the car, I'm not sure if I should post detailed info about it since it is for a competition and all. I don't think I explained the functionality of this circuit well enough, let me try again. The circuit has a constant 12v running through it but when it recieves a 12v signal it cuts the constant 12v after a timed delay. Also, my problem with multisim wasn't so much that it didn't work but rather it set the timestep to low and was opperating in milliseconds instead of seconds.
edit: the pot would be used in a circuit like this one http://circuitos.tripod.cl/schem/r84.gif |
09-08-2005, 01:31 AM | #9 | |
Cooling Neophyte
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09-08-2005, 02:43 AM | #10 | |
Cooling Savant
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If a seperate input is it a pulse? |
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09-08-2005, 08:19 AM | #11 | |
Cooling Savant
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09-08-2005, 09:13 AM | #12 |
Pro/Staff
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Can you just use a simple PIC chip?
Just to clarify our understanding: 1) You have a constant +12V power supply to the circuit and Ground 2) You have a +12V input signal to the circuit that will initiate a timer. 3) The timer, when complete, will interrupt a +12V line supplying power to another section of the overall design 4) You require some analog control over the length of the timer (simple pot, probably) 5) You require some method to reset the circuit, such as a reset button To do this, you need several "inputs" to the circuit: 1) +12V PS 2) 0V GND 3) +12V SIGNAL 4) +12V INTERRUPTED LINE Potentially, you could have separate grounds, but that is negotiable. Mogwai is probably on the right track if you want discrete components. It's cheaper and faster if you know component design instead of microchip programmming. Simply use a switch to toggle a flip flop that initiates a current limited feed into a capacitor. The capacitor voltage is then compared to a reference voltage given by a pot (your timer control). When the comparison reaches "true", the comparitor sends voltage to a transistor which interrupts the +12V INTERRUPTABLE line. There's more to a good design, of course. You'll want lots of signal conditioning if it is in an automotive environment. Also, pay good attention to your grounds! Do not skimp on components, as a blown transistor is a pain to replace on race day. Etc... etc... Good luck. |
09-08-2005, 09:17 AM | #13 |
Cooling Savant
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so it has a consant 12v input going through it, and when it recieves another 12v 'control', it allows the original constant 12v to continue through for a specific length of time, based on the setting of the pot. Once the timer expires, the 12v 'feed-through' is cut.
Am I understanding this correctly? If so, what do you want to happen once the timer has expired, and 12v 'feed-through' has been cut? The state of the circuit at that point is, you have a constant 12v going into the circuit, but not being passed through. You have a 12v 'control' voltage set to TRUE, your pot is set to the preveous setting, and the timer is expired. <edit> hehe, crosspost.
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When you do things right, people won't be sure youv'e done anything at all. Looking to buy/trade for used Deep Fryer and Vacume Pack Sealer. |
09-08-2005, 02:09 PM | #14 | |
Cooling Neophyte
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09-08-2005, 03:05 PM | #15 | |
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09-08-2005, 05:14 PM | #16 | |
Cooling Neophyte
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You can use a uC with an ADC built in so you can use your pot Microchip is very good with free samples. http://samples.microchip.com/ I like the pic16f88 from their mid-range series. I have used it with this boot loader: http://www.etc.ugal.ro/cchiculita/so...bootloader.htm I don't think Vector86 knows much about microcontrollers though, since if he did he would not be asking how to do this. It took me a few weeks to read all the manuals, datasheets, application notes, learn the assembly instructions, and figure out how to use mplab and the simulator. Puting something together with descrete components would be faster than learning all that...BUT if you have the time, I suggest you do. Microcontrollers are amazingly useful. After I finished my senior project using some microcontrollers, I felt like I could build anything. Microchip has TONS of docs on their stuff. Vector86, if you decide to go the uC route I can help you by pointing out the pdfs you should read. |
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09-09-2005, 12:11 PM | #17 |
Pro/Staff
Join Date: Oct 2001
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You are probably right in thinking Vector86 isn't versed in uC designs.
As for PIC chips, they are great beginner chips. For advanced use, motorola and TI have some even better chips but they really require a bit more experience, because there isn't the same amount of community support for them. Some TI microchips have truly amazingly low power usages and still outperform PIC chips but they are kind of a pain to program. Etc... Well, good luck, Vector86. |
09-10-2005, 01:54 AM | #18 | ||
Cooling Savant
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Yes Quote:
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09-10-2005, 10:14 AM | #19 | |
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09-10-2005, 11:48 AM | #20 |
Cooling Savant
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I did some reading on the PIC chip, it's way too complicated for this job. This circuit needs to be very simple. Brian256, I do have basic electrical knowledge, just not with some of the more advanced ICs. Another bit of info I should throw in: this circuit is a backup for the in dash unit that performs the same task, hence, it doesn't need to be as complicated.
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09-10-2005, 02:33 PM | #21 | |
Cooling Neophyte
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You do know how comparators, capacitors, resistors, and diodes work right? |
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09-10-2005, 05:35 PM | #22 | |
Cooling Savant
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09-10-2005, 07:06 PM | #23 | |
Cooling Neophyte
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Get a breadboard and play around with this stuff, thats how I figured it out! |
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09-11-2005, 03:29 PM | #24 | |
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Mogwai has a great suggestion. Get some of these parts, breadboard it up, and try it out. I think you'll learn a lot more than just trying it out on a simulator. |
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09-17-2005, 07:24 PM | #25 |
Cooling Savant
Join Date: Jun 2002
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I breadboarded it up with an lm339 but I couldn't get it to work the way I want it to. Is there anything I should look closely at?
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