Ok, you guys blazed through my last question like it was a late night burger from Jack in the Box, so lets see what you have to tell me about this one...

We are looking to switch our maximum 1.2v signal on and off several times a second, say a maximum of 3 times per second. We were told analog timers would not switch such a low voltage, and that an eprom may be what we need.

From my automotive understanding, an eprom is just a memory device, and doesnt perform a physical task other than holding data. We may have been given bad advice, i dont know. What do you guys think?

The timer doesn't have to be especially accurate, and it would be nice if we could adjust the on/off intervals. A 12 volt power source is handy, so if it needs to have an external power source thats cool.



Thanks again for the great info guys, I really appreciate the help.

 

There are several ways this could be done, for your application.

Essentially, you need an electrically-controllable switch and a square wave or pulse generator circuit to control it.

Alternatively, you could use an "analog multiplier" IC and multiply your voltage by a square wave or pulse that alternates between 0v and 1v (or 0v and 10v if the analog multiplier is a divide-by-10 type, such as the AD633).

And there are probably other ways to do it.

AT any rate, we would probably need to know what the switch's output will be driving. i.e. What does it connect to, next, "downstream"? Or, what is the resistance or impedance of whatever it will be connected to? And does that device care if it's connected to nothing, when your voltage is switched off, or should it be connected to 0v/ground during the off intervals?

The controllable switch could be a mechanical relay, or a solid state relay, or a transistor (BJT, J-FET, OR MOSFET) circuit, or an "analog switch" or "analog multiplexer" IC circuit, or maybe something else.

The details of the square wave or pulse generator circuit that will turn the switch on and off will depend on what kind of voltages and current are needed by the switch's control input, which depends on what type of switching circuit is used. But you could probably use a "555" timer IC, or a comparator or two, or even opamps, configured as a pulse-generator circuit (probably with with variable duty-cycle and frequency, so you could change the ratio of the on-time versus off-time, as well as the switching rate). You can find those types of circuits in the datasheets for the LM555 (NE555-compatible) and the LM339 or LM311, et al, at national.com, for example, and many more pulse generator circuits elsewhere on the web . But you will need to make sure that the circuit you eventually use will output the upper and lower voltages needed by the control input of the switching circuit you end up using, and also that it can deliver the current the switch's control input might need.

Is +12VDC the only power supply voltage that is available? And how much current can it supply, maximum?

- Tom Gootee

http://www.fullnet.com/~tomg/index.html

-

 

I'm kinda workin on a similar project, I would try a 555IC with a 1000uf capacitor and two 300 ohm resistors in paralell, It pulses pretty quick. Too low of a resistance stalls it tho. This is only a suggestion, I'm a novice myself but the people in the forum would know how to do it if that does'nt work. Good Luck.....

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A 555 doesn't need low resistance and high capacitance. You can get exactly the same results with 150kohms and 1uF, or 1.5Megohms and 100nF.

__________________
Ron

 

Excepting that in different environmental circumstances said circuits will produce very different results. Never forget, IC's and passive components are REAL WORLD devices, and their function depends on the REAL world.

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This device will be switching the third voltage in a non inverting voltage summer circuit to alter it's final output.

A datalogging device will be monitoring the voltage summer output, so long story short, i'd have to ask an engineer to give me specific values, but i'd assume the load is next to nothing.

The 12v power supply were using to test on is a standard car battery, and should have all the power we need and then some.

Can I provide any more details to get you guys aimed in the right direction?

 

hi evotec1

>> We are looking to switch our maximum 1.2v signal on and off several times a second, say a maximum of 3 times per second. We were told analog timers would not switch such a low voltage, and that an eprom may be what we need.

Who told you that an analog switch would not switch a +1.2Vsig??

You require a 555 timer, as a pulse generator, driving a 4066 analog switch.
Switch the +1.2Vsig thru the 4066 analog gate, it will all work on +12V.

Does this help?

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Eric
"Good enough is Perfect"

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