I'm looking to build a simple 1mv peak to peak square or sawtooth generator that will fit in my shirt pocket. I'd like the frequency around 65hz. Should I use a timer or does someone know of something simpler?

Any help will be appreciated.

tacHammer
arklamed@sbcglobal.net

 

I'm just curious why you would want a 1 millivolt signal generator.

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Ron (aka Rube)

 

Can you just generate a regulator wave, step it down with a resistive divider buffered by an op-amp buffer followed by a AC pass capacitor (to remove offset from the op amp, since 1mV is pretty damn small compared to the mV-order offsets on most op-amps). 65Hz is really slow so I would think a capacitor timer, like a 555 timer would be best.

 

I want this for a simple ECG simulator that will fit in my pocket. 1mV peak to peak is about the normal size and 65-70hz would be perfect to test telemetry transmitters. The waveform doesn't have to look like an ECG. It wouldn't matter if it was a square wave or a triangle wave.

Pocket sized ECG simulators cost $1,400.00 and that's not an affordable option.

Thanx for your reply.

 

Is that the required bandwidth of an ECG channel? It's about 60 times a normal pulse rate (60-70 beats/min).

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Ron (aka Rube)

 

Ha! You are so right. Correction apprecaited. 65-70bpm is what I meant not 65-70hz. Sorry.
Rick

 

Is this a one-off, or do you need a robust design that doesn't require any adjustments? Does it need long battery life? Can you use surface-mount parts, or do you need to use common thru-hole parts?

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Ron (aka Rube)

 

If I had a unit that is small enough I can deal with it not being adjustable. I just need something simple that will run around 60-70bpm. Battery life is not important. I'm not sure that I would be able to use or solder SMD's with my eyes that are over 50 years old. (c: I'd prefer thru-hole parts.

Thanx,
tacHammer

 

Just use a 555 timer to generate your signal, then a simple resistive attenuator to drop it down to 1mV.

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PIC programmer software, and PIC Tutorials at:
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Why are they so expensive? Do they do anything else besides generate a 1mV 1 Hz square wave?

Update: Here's one that's a bargain at only $250:

http://www.ecgsimulators.com/prod02.htm

 

Thanx for your reply. What you can't see in that photo is the unit is laying down and is much larger than it appears in that picture. I have a simulator that is smaller than that one but what I want is one that will fit in my shirt pocket.
The $1400 unit will do much more than just emit a 1mV wave at 60-70bpm. You can adjust it from 30 to 120bpm and from .5mV to 2mV and it even has arrhythmias built in. I have a simulator that can do all that if I need it but I just want something that can simply use to test whether a telemetry transmitter is working or not by putting a waveform on the central station monitor.

If I wasn't so lazy and hairy chested I could just put electrodes on myself.
I guess that's what I should consider.

 

Sounds like this is an opportunity for a uC project. The size would only be determine by the user interface (leds, buttons) and connectors and the battery. Hmm.... (can you hear the wheels turning?)

 

Here's a 555 circuit, like Nigel suggested. It should run on a couple of AAA's for months (years?).
There are several CMOS 555 models - TS555, LMC555, ICM7555, ZSCT1555, etc.

Attached Images

ecg test osc.PNG (11.9 KB, 15 views)

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Ron (aka Rube)

 

That's perfect! Thanx Roff.

 

tacHammer,

From a former Biomed Tech...a LM555 EKG simulator was a project I built in my Medical Electronics class back in 1974. What goes around comes around.

Ken

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"To invent, you need a good imagination and a pile of junk."
Thomas A. Edison (1847 - 1931)