# Pulsing Switch?

• 11-15-2010, 09:27 AM
danimal
Pulsing Switch?
How hard would it be to create a simple piece of hardware that would put out a adjustable pulse rate when a switch is turned on?

I would like to use something like this in my air ride setup to control the flow rate of air to lift or lower the vehicle by quickly pulsing the valve open and closed at an adjustable rate to speed up or slow down lift when the button is depresed.

Any Input would be Greatly appreciated.
• 11-15-2010, 01:26 PM
OldSpark
How do you want to adjust it?

Variable resistor? A 555 PWM circuit? eg:
http://img51.imageshack.us/img51/924...ulatorpwmu.gif
• 11-15-2010, 02:01 PM
danimal
I know im asking a partially complicated question, but I'm mildly limited in my electrical knowledge, so I might need a bit of coaxing to understand some of this, but always wanting to learn!

Id like to be able to actively control it on the switch box, but not sure how that would be done?
• 11-15-2010, 02:39 PM
OldSpark
It depends on what you want - ie, what is required.

The "555" is an Integrated Circuit aka IC or chip. Specifically it is an 8 legged timer chip (8 pins) that can do one-off delays (monostable) or pulse trains (astable). (It can also be used or "tricked" to do other things...)

How it behaves depends on how you connect external components.
And component size determines time or frequency.

In the above diagram, the LHS capacitor (C) and resistor(s) (R; R1-R3) combination set an astable frequency of about 400Hz. IE - a square wave (on-off-on-off...) of about 400 cycles per second.
But in that particular connection, varying the volume control (ie, R2, the variable resistor aka potentiometer aka pot) varies the Duty Cycle from zero to 1.
IOW, the ratio of its ON time to total time (on & off) varies from 0% to 100%.
If 0%, it is on 0% of the time (ie, off).
If 20%, it is on 20% of the time, ie, 20/100 = 1/5th of the time.
If 10%, it is on all the time.

So if it was controlling a light or LED, the light would be on from 0% to 100%, hence (presumably) varying its brightness.

There are some technicalities like what the other pins do, and that it doesn't quite reach zero nor 100%. But who cares? (....at this stage.)

The above variable Duty Cycle technique is known as PWM - Pulse-Width-Modulation. (IE - we vary the relative Pulse Width; modulate is a fancy term for change or vary - you modulate your stereo volume with the loudness knob. (Do it in sync with the beat and it drives others nuts!) )

PWM assumes you can do what you want like a dimmer switch or volume control.
But unlike a "pot" type volume control or dimmer that can be used on ordinary lights (eg, tungsten bulbs; ordinary dash lights etc), some things like CFLs or LEDs cannot, so PWM may be used.
(Though some things like LEDs and halogen lights can use pots, they are not linear - ie, volume 1-10 is not brightness 1-10; LEDs & halogens may go from a bit bright (1) to fully bright (10) with pot between 8 to 10. That's because of LED's & halogen's voltage behaviour. PWM however is a constant ON voltage, but varies the current thru the device; hence achieving dimming but in a linear fashion. Usually.)

Instead you might be asking for a one-shot of varying delay.
EG - to rise 1" is 1 second "on". 10" is 10 seconds.
So then dial the knob (R2) and hit the GO button.
That requires a change to the above circuit. EG - the same sort of components, but different values and different connection. And the GO button would be to pin #2 (probably).

There are various techniques and methods (eg, the PWM fan controller MIC502; or 4017 counter; etc).
It depends on what is required.

The above is an example for a DIY solution - you obtain and fit the components etc.
• 11-15-2010, 02:42 PM
justchat_1
555 timer is the way to go (like OldSpark recommended)...

Only issue I could see here is your talking about a solenoid. Switching time of the solenoid is quite a bit slower then most PWM circuitry operates at. So you may end up with a rather jerky raise/lower instead of a slower smoother one.
• 11-15-2010, 06:05 PM
danimal
Thanks OldSpark! Great Breakdown

&thats what I was thinking as far as the solenoid goes, that it couldn't react fast enough. Basically now if i want to lower slow i will tap the rocker repeatedly very quick on and off resulting in pss.. pss.. pss.. dumping of air instead of all at once, but i would like to be able to hold the dump down and have the same effect, but be able to vary the on off time like old spark said.

There is a system like this on the market, but there controller costs upwards of a \$1000 as opposed to a \$50 rocker switch box....
• 11-15-2010, 07:01 PM
OldSpark
No - nothing as cheap as \$50.
More like \$10. How's that? (LOL!)

Price depends on hardware - as in the box & switch etc.

Depending on the solenoids, I see the circuit as being cheap - say \$5 for a 555 and the various components (caps, pot etc).
Maybe another \$5 for "power conditioning" - voltage regulator & things to ensure spikes etc do not destroy the 555.

Add to that the output "driver" - maybe a \$3-\$5 relay or MOSFET (transistor).

Then the box, and switch(es) and knob...

VIZ:
- a knob to dial in the delay time;
- an adjacent switch to "actuate".
On whatever box or where ever you want.

Though a simple push-button will do, there is nothing preventing it being a missile-switch with "Warning..." sign etc. Even flashing lights and buzzers - but for that I recommend a 2nd switch to "deactivate wanker devices". (Wanker is (usually) a non-offensive term here. Substitute show-off or bling etc if desired.)

As usual with these things, the circuitry itself is cheap.
To build a "proper" PCB can be expensive, but these are often built on vero-board or matrix-board etc.
But it's the enclosures and switches and connectors and that sort of "hardware" that costs a lot.

And there are variations.
EG - instead of a variable pot, you could have a rotary switch or successive (DIP) switches that change the resistance. That's good for discrete settings - like dialing in Warp Factor 8 instead of 7.846.
(A rotary switch can be used with a 4017 "one of ten" counter as a "divide by n" counter, but that's another implementation that is added on to the 555 as a clock = astable.)

For monostable 555 "push to fire" samples, maybe see here (though I suspect that circuit is errored - the 555 is unpowered when the switch opens....) or its followup here. (They were just my first 2 google returns for "555 monostable circuit", but later comes an old classic reference kpsec-555timer.)

I suggest for starters a simple pot-type 555 test circuit.
And for that, some questions:

- the shortest and longest time required (eg 0.5secs to 7 secs)?

- the current of each solenoid (whatever) - I suspect a few Amps each?

- all solenoids together? Or 2x2?

- can the solenoids be ground switched? (ie, other end to +12V, switch on ground circuit?)
(or doesn't it matter)

I assume a 2-way selector else 2 circuits - ie, one for up, one for down?