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Momentary Gate Switch

I will try my best to explain what im trying to accomplish. I'm using a momentary switch to trigger a solenoid valve to release air pressure in a home made potato gun. I have found that you can get multiple bursts out of the gun if you flick the momentary switch very quickly. The pressure decrease is small enough to shoot multiple objects without re-pumping which would be very convienient and much more efficient then exhausting all the excess pressurized air.

I am looking to make a circuit that would create a square wave for about a tenth of a second when the momentary button is pushed. The input is 18v in a series of two 9v batteries. The output should also maintain the 18v difference.

I'm not sure what to call the switch im trying to make and am not sure if it is in the correct group, however any information you could throw my way would help considerably.

thanks, dave

birmingham, al

Reply to
shoeInsertsForDummies
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It's usually called a pulse generator or one shot. From your description of your application I assume you don't really want a square "wave" but want a square "pulse" instead. If that's the case a simple

555 timer can be used to create a one shot circuit where the output pulse width is constant regardless of the input pulse width:

formatting link

Reply to
slebetman

Excellent. The equation is t = R1*C1, so im assuming that a 100k resistor and a

1uF cap would create a pulse of .1 seconds. Is that correct?

thanks, dave

Reply to
shoeInsertsForDummies

It's called a "one-shot" and we would need to know how the resistance of the solenoid to pin down an exact circuit, but it may be something along the lines shown below made from Radio Shack components. The other circuit in the web link is a fiction- doesn't work. View in a fixed-width font such as Courier.

. . . . |9V 1N4001 . .---------------------------||----------------|>|---+----+---. . | | | S | . | 1N4001 1N4001- S | . +--|>|-----+----------+----+-----------. ^ S | . | | | | 0.1U | | S | . | | [1K] === | | | |+ . | | | +--[1M]-----+ | | === . | | | | | 555 | | 100U . | | | | ---------- | | 35WVDC . | | | | | V+/RST | | | | . | | .-+ | | CNT|-N/C '----+ | . ---9V .---+ | | +-[1K]-|DIS | | | . - | |+ SW o | | | | d| | . | | === -| | '------|THRESH | IRF510|- | . | | |1U o | | OUT|---+-----|< | . | [100K] |16WVDC | '-----------|TRIG | | |- | . | | | .----+ | | | s| | . | | | | | | GND | [10K] '---+ . | | | [10K] === ---------- | | . | | | | |0.1U | | [220] . | / | | | | | | | . '-o o--+---+---+----+------------------+---------+-----------' . on/off . . . . . .

Reply to
Fred Bloggs

It would be better to make the ON/OFF switch a SPDT to discharge the solenoid capacitor in OFF, and add a DIScharge momentary to either use conventionally or blow the tank before storage: View in a fixed-width font such as Courier.

. . . . |9V 1N4001 . .---------------------------||----------------|>|---+----+---+---. . | | | S | | . | 1N4001 1N4001- S | | . +--|>|-----+----------+----+-----------. ^ S | | . | | | | 0.1U | | S | | . | | [1K] === | | | |+ | . | | | +--[1M]-----+ | | === | . | | | | | 555 | | 100U | . | | | | ---------- | | 35WVDC| . | | | | | V+/RST | | | | | . | | .-+ | | CNT|-N/C '--+-+ | | . ---9V .---+ PULSE| | +-[1K]-|DIS | | | | | . - | |+ SW o | | | |IRF510 d| | | | . | | === -| | '------|THRESH | |- | | | . | | |1U o | | OUT|---+---|< | | | . | [100K] |16WVDC | '-----------|TRIG | | |- | | | . | | | .----+ | | | s| | | | . | | | | | | GND | [10K] '-----+ | . | | | [10K] === ---------- | | | | . | on | | | |0.1U | | | [220] | . +--o | | | | | | | | | . | o-+---+---+----+------------------+---------+-----------' | . | / | | . | o-------------------------------------------------------------' . | off DIS | . | SW o . | -| . | o . | | . '--------------------------------------------------------' .

Reply to
Fred Bloggs

This connection is more logical- when the ON/OFF is OFF it can't do anything, you have to be in ON position to pulse or discharge: View in a fixed-width font such as Courier.

. . . . |9V 1N4001 . .---------------------------||----------------|>|---+----+---+---. . | | | S | | . | 1N4001 1N4001- S | | . +--|>|-----+----------+----+-----------. ^ S | | . | | | | 0.1U | | S | | . | | [1K] === | | | |+ | . | | | +--[1M]-----+ | | === | . | | | | | 555 | | 100U | . | | | | ---------- | | 35WVDC| . | | | | | V+/RST | | | | | . | | .-+ | | CNT|-N/C '--+-+ | | . ---9V .---+ PULSE| | +-[1K]-|DIS | | | | | . - | |+ SW o | | | |IRF510 d| | | | . | | === -| | '------|THRESH | |- | | | . | | |1U o | | OUT|---+---|< | | | . | [100K] |16WVDC | '-----------|TRIG | | |- | | | . | | | .----+ | | | s| | | | . | | | | | | GND | [10K] '-----+ | . | | | [10K] === ---------- | | | | . | on | | | |0.1U | | | [220] | . '--o | | | | | | | | | . o-+---+---+----+------------------+---------+-----------' | . / | | | . o-------------------------------------------------------------' . off | DIS | . | SW o . | -| . | o . | | . '-----------------' .

Reply to
Fred Bloggs

Almost. You have to think about what is happening in an analog sense. The time you get from R1*C1 is the time it takes the C1 to discharge into R1 down to the level of .3679 of what it was to start with. If you start with C1 charged to the logic level of +5 volts and if you are discharging it into R1 and if you are watching the voltage on C1 with a comparator that has a threshold set to 1.839 volts, then the comparator will flip .1 seconds after the discharge begins. If the comparator threshold is set to some other voltage, then the switching time will change accordingly.

-Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

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