I have devised a very simple circuit that most people could make without a circuit diagram. (I hope
). It is based around a pre-programmed ROM. This I am afraid you will have to make for yourself. Do people still have the facilities for blowing their own ROMs or am I showing my age?
The MSBs of the ROM are connected to a Hex switch to selects various waveforms which are programmed in to the ROM, these are cycled round using a variable speed clock (555) and counter connected to the LSBs. Then a D to A and filter gives you your output.
Not fancy, simple and basic, no need for complicated C programming etc., but what do you expect for homebrew. If you want random ectopics etc, pay the companies for their fancy boxes.
If you want lots of leads at once use lots of ROMS in parallel or just put different filters on the output if you do not need vastly different shaped waves. (And why do you?)
I have even seen analogue simlulators that used a few linked and half-wave rectified oscillators to produce the P, QRS and T-waves. I challenge anyone to build that from scratch these days. Again with multiple outputs from the one source waveform.
To programme the ROM draw a few waveforms on graph paper and then work out the values at enough time intervals. You do not need many, you are dealing with very low frequencies so can filter out the noise. And if it comes through, so what? You are making a test box not a diagnostic tool.
Contact me if you want more details
Robert
PS Why do people want all these ECG simulators? Does anyone actually test waveform analysis systems? If you just need it for a go-nogo test of leads and monitors why not use a low frequency signal from a signal-generator? It might not look correct on the screen but it does the job.
