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#1
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Hold circuit
Hi,
my problem ist the following: With a foot contact I switch a tiny power mosfet (BS 170) on, which in turn (softly) turns on a small 9V DC motor. After a moment, my foot often gets tired, and I would like some circuit to hold the gate of the mosfet positive for me. After a minute or two, I would like to be able to turn off my mosfet again by a short touch to the pedal. I was thinking of a combination of 555 timer(s) opening a time window where I could take the foot off the pedal, and a sample an hold ic, but do not see how to combine them, I am just an amateur... Is there a genius out there who can help me to accomplish this? Any input will be greatly appreciated, thank you in advance! Ernesto |
#2
Posted to alt.electronics
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Hold circuit
On 2009-01-08, Dr. Ernst Baumgartner wrote:
Hi, my problem ist the following: With a foot contact I switch a tiny power mosfet (BS 170) on, which in turn (softly) turns on a small 9V DC motor. After a moment, my foot often gets tired, and I would like some circuit to hold the gate of the mosfet positive for me. After a minute or two, I would like to be able to turn off my mosfet again by a short touch to the pedal. I was thinking of a combination of 555 timer(s) opening a time window where I could take the foot off the pedal, and a sample an hold ic, but do not see how to combine them, I am just an amateur... Is there a genius out there who can help me to accomplish this? Any input will be greatly appreciated, thank you in advance! assuming your switch has dual-throw contacts .-------------------------------------------------------------. | This is an ascii schematic, if the diagram appears garbled | | try switching to a fixed-pitch font (courier works well) | | pasting it into notepad works well on ms-windows. | | or in google groups "show original" (in "more options") | `-------------------------------------------------------------' +9V +---------------+--+--------. | X| | | | .-----+ | | | | | | | ===== | [47K]| . . . .|. . . . |10u | | | . VCC(8) . | |1u | | . . out +-----+ ===== | `--RES(4) OUT(3)----+----- | | | | . 555 . | | .-|--o-_ +-----+-----TH(6) DIS(7)-- | | | | -o--+ | . . | | [1K]`--o `-----TR(2) CV(5)-- | | | . . | | \ . GND(1) . | | \| . . . .|. . . . | | |--[10K]-------------------|----------' | |/| | [220K] /~ NPN (eg BC547/2n3904) | | | | `---+-----------------------------+ 0V |
#3
Posted to alt.electronics
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Hold circuit
On Fri, 9 Jan 2009 00:25:16 +0100, "Dr. Ernst Baumgartner"
wrote: Hi, my problem ist the following: With a foot contact I switch a tiny power mosfet (BS 170) on, which in turn (softly) turns on a small 9V DC motor. After a moment, my foot often gets tired, and I would like some circuit to hold the gate of the mosfet positive for me. After a minute or two, I would like to be able to turn off my mosfet again by a short touch to the pedal. I was thinking of a combination of 555 timer(s) opening a time window where I could take the foot off the pedal, and a sample an hold ic, but do not see how to combine them, I am just an amateur... Is there a genius out there who can help me to accomplish this? Any input will be greatly appreciated, thank you in advance! --- View in Courier: +V--+---------+-----+------+-------+------+------------+ | | |K | U1 |8 | U2A| [10K] [100K][1N4148][1M] +---+---+ | +---+---+ | | | Rt| 2|_ Vcc |3 +-------O|S Vcc | D +-[0.1µF]-+-----+------|--O|T OUT|--|--------| Q|--G BS170 | | 6| | | | HC74 | S | +---|TH 7555| +-1M-+--O|R _| O | | 7|_ _|4 | | +-|D GND Q|-+ |--S1 +--O|D R|O-|----+ | +---+---+ | O | | | GND | | | +-----|-----+ | | +---+---+ | | | | |+ |1 | [0.1µF] | | [1µF] | [0.1µF] | | | Ct| | | | | GND-+----------------------+-------+------+----+-------+ | U2B | +-------+ +--O|S | +---| HC74 | +--O|R | +---|D | +-------+ U1 is a CMOS 555 timer which puts out about a 1.5 second pulse (with Rt and Ct as shown) when S1 is made. U1 isn't retriggerable, so as long as the switch is released before U1 times out, the contact bounce on release won't cause another pulse to be generated. U2A is a "D" type flip-flop wired to toggle on successive high-going edges at the clock input, and is reset on power-up by the 1 megohm resistor and the 0.1µF capacitor, as is the timer, guaranteeing a low input to the MOSFET gate. In use, once power is applied to the circuit, S1 is tapped, which will cause the motor to start turning and then tapped again some time later in order to stop the motor. Tapping it again will cause the motor to start again and tapping it after that... JF |
#4
Posted to alt.electronics
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Hold circuit
Would a 'push on / push off' switch work?
*************************** "Dr. Ernst Baumgartner" wrote in message ... Hi, my problem ist the following: With a foot contact I switch a tiny power mosfet (BS 170) on, which in turn (softly) turns on a small 9V DC motor. After a moment, my foot often gets tired, and I would like some circuit to hold the gate of the mosfet positive for me. After a minute or two, I would like to be able to turn off my mosfet again by a short touch to the pedal. I was thinking of a combination of 555 timer(s) opening a time window where I could take the foot off the pedal, and a sample an hold ic, but do not see how to combine them, I am just an amateur... Is there a genius out there who can help me to accomplish this? Any input will be greatly appreciated, thank you in advance! Ernesto |
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