Activation switch question

[Toolmaker]

I am not sure if this is the correct forum and i apologize if it is not.
I need to hook up a switch that will turn on a pump to spray material for a certain amount of time, kind of like a one time shot of lube.
The mechanism goes up and down so as it comes down, let's say 1/2" before it contacts the material, it hits a switch to activate a small 12 volt pump to spray the material then stops. The mechanism goes back up and the whole process is repeated. I hope i have explained this good enough for you to understand i will be using a small 1GPM Flotec pump 12 volt that will have spray nozzels in position.
Thank you

[smarbaga]

maybe post a picture, worth 1000 words

[Bear]

Hi,
sounds like you need a commom micro switch,
with a ramp?
Bear

[HuFlungDung]

Do you need an accurately timed (but with user modifiable) ON interval? Timer modules are available....I can look one up for you if you need it. They will cost you nearly $110.

[Toolmaker]

Originally Posted by Bear Hi, sounds like you need a commom micro switch, with a ramp? Bear

Yeah, this is what i was thinking. It does not have to be that precision i am using a weed sprayer that has a 15 gallon tank and a 12 volt pump.
It is a hydraulic machine with 6 inches of travel, like i said i need it to lube at around 1/2" before the punch (which is on the end of the cylinder) Makes contact with the material. It only has to spray for about 3-5 seconds then shut off. But i need a way for the switch not to activate when the cylinder comes back up. The picture suggestion is a great idea, i will see if i can get some up here

[Al_The_Man]

You need a one-way-activated micro switch, this switch activates in one direction only, the striker is active in one direction and on the reverse, inactive.
One version is BZE6-2RN28.
Al.

[gar]

051128-1456 EST USA

Toolmaker:

Another way to get your trigger pulse only on advance is to use an ordinary switch or prox switch and logically AND this with your advance signal. The advance signal will not be present on the return stroke. Use a leading edge detector if required.

If you want spraying to continue until you start to return, then no timer would be required with proper actuation of the switch.

A simple way to get your timing function is with a Signetics 555 timer in single shot mode driving an isolated output relay. Timing is easily adjusted with a variable resistor.

If your trigger switch remains on as long as the head is advanced, then you will need a leading edge detector if you want only a short burst. I believe the 555 requires a trigger pulse shorter than the output pulse width.

The leading edge detector is simply an RC differentiating circuit with two diode to prevent excessive negative and positive voltage to the single shot. You will have to phase things correctly for the devices you use.

To do these things you will need electronics experience or get help.

(edit 051128-2043) I am now where I can look at a 555 data sheet. The 555 goes high for the output pulse, and requires a negative trigger pulse. Neither the standard 555 or the CMOS version have much pull-up current capability. I would suggest the CMOS version and directly drive a 2N7000 for the output. If you can find a suitable solid-state relay to control the motor I would prefer this. You did not indicate whether the pump motor was AC or DC nor its current requirement. This may determine the choice of an output switch. A solid-state switch may need transient protection on the output side. None required on the input side. If you use an electro-mechanical relay, then its coil must be paralleled with a back biased diode to protect the 2N7000.

The 555 triggers on the leading negative slope of the trigger pulse.

See National Semiconductor www.national.com and search for LMC555, then pick datasheet. You can find the standard 555 datasheet at www.fairchildsemi.com. Search for LM555 or NE555 or SA555.

The CMOS monostable (single shot) time constant is about 1.1 x R x C. For C = 10 microfarads, T = 3 sec, then R is about 300 k.

(end edit)

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