From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-08-09 11:05:07
Hi,
----- Original Message -----
From: <gogol101_at_yahoo.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Thursday, August 09, 2001 10:46 AM
Subject: [buildcheapeeg] comADC-EEG - 16 bit DAC
> Hi Joerg,
>
> yesterday I looked at pages about Timer 555 ( bought 2 pices)
> http://www.uoguelph.ca/~antoon/gadgets/555.htm
>
> I'm fascinated how this 30 old years NE555 can do nice work.
>
> And I have this idea:
> Is possible add 16 bit dig. counter ( or 2 x 8bit ), I think also
> cheap.
> Time resolutin would be high, I read that new 555 reached output
> frekvency at about 2.4 MHz.
2 cheap asychronous counters would be ok.
You need a 16 Mhz (or whatever the counters can manage)
crystal oscillator to generate the clock for the counter.
The 555 would generate a gate time for the 16Mhz clock.
If the gate time is 1 ms maximum you will get about 14 bit resolution.
(However the resolution is limited by stabiltity of Ub, the cheap
constant current source, etc)
> And is possible to read this counter by parallel port ?
You can read the counter when it has stopped via parallelport.
Or you could use a counter with a shift register and read the
result with 2 handshake lines from the com-port.
(one for shift clock out and one for counter data in)
The isolation can be done easily if you place the counter etc.
behind the optocoupler on the PC side.
> (please, don't laugh me if I'm naive, I have one more idea )
Your idea seems to be quite realistic.
Regards
Joerg
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