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guanming
Joined: 11 Aug 2006
Posts: 2
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 Posted:
Fri Aug 11, 2006 4:26 pm Post subject:
will window comparator work here? |
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Good day people.
I've got some problem doing one of my project.
And here goes,
I am building a touch base input device for my project. And basically i came up with this idea of using a window comparator for the application.
The list of component used:
- touchpad (is basically a copper tracing which is a open circuit at first, refer to figure 1)
- LM741 op-amp x 2pcs
- 1kohm resistor x 2pcs
- zener diode x 2pcs
- 7408 AND GATE x 1pcs
The result i wanted was that once i touch the touchpad, the output from the AND GATE must be a logic 1 and once i let go, it ouput must be a logic 0. (im comparing 6v and 1v respectively n' not 5v and 1v)
And i tried quite a number of method to no avail.
Am really quite stuck down by it.
Any help would be grately appreciated
figure 1: the touchpad
figure 2: before implementing the touchpad to the window comparator
figure 3: added in the touchpad to the comparator circuit
THANK YOU
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neon
Joined: 25 Feb 2006
Posts: 594
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Sat Aug 12, 2006 3:30 am Post subject:
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| you have too many parts for it. try an LM139,.239,339 these are real comparators LM741 is a good operational amplifier not a comparator even at open loop gain. as long you hold it it will stay one way when released it will revert i think you need a flip-flop not a gate but then again maybe that is what you want Zeners take them out tie a simple diode to +5v as a clamp. or use cmos all the way. And finaly your circuit does not have any bias how how can you decide at power up which way the amps will swing since one input is open at all times.for a window of 1 to whatever you only need one not 2 amplifiers just set the bias point from power do not let inputs float ever. |
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guanming
Joined: 11 Aug 2006
Posts: 2
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Sat Aug 12, 2006 5:28 am Post subject:
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| neon wrote: | | you have too many parts for it. try an LM139,.239,339 these are real comparators LM741 is a good operational amplifier not a comparator even at open loop gain. as long you hold it it will stay one way when released it will revert i think you need a flip-flop not a gate but then again maybe that is what you want Zeners take them out tie a simple diode to +5v as a clamp. or use cmos all the way. And finaly your circuit does not have any bias how how can you decide at power up which way the amps will swing since one input is open at all times.for a window of 1 to whatever you only need one not 2 amplifiers just set the bias point from power do not let inputs float ever. |
neon, maybe this is too much to ask from you but can you like draw out the schematics for my reference? i really need it urgently... thank you so much in advance. thank you again.
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neon
Joined: 25 Feb 2006
Posts: 594
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Mon Aug 14, 2006 5:33 pm Post subject:
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| I rely don't quite understand what you want. The way you wrote it sound like I hold my thingers on it it woks i release it doesn't work? or do you want one touch turn it on another touch turn it off. which way you want this thing to operate? let me know before you ask for help. OK?Leave your e-mail and i will send you what you want ok? |
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