Some ideas for modifying HAL-4 (cf. manual):
1. Simply changing R25 (47 ohm) to e.g. 120 ohm decreases (and balances)
power drain and still enough to drive LED1 and TIL111 opto coupler (as I use
it now).
2. 9V battery can be omitted (like all well-educated mice have done it;-))):
connect green phone cable (from Pin 2, TX, not used) to DTR (Pin 20) of
serial connector. It's important to put a diode (open direction from serial
connector to HAL) before the green cable to protect HAL from negative volts
(RS-232 works using +/- voltages, practically +/-12 V on PCs). If DTR is
active and pulled up to +12 Volts, it ensures the required current (< 20 mA)
for the
7805 regulator (HAL's 'opto-separated part' to the PC) and drives MAX232.
For
this, also connect the 3rd pin (to green cable) of the phone jack to the 9V
battery connector (pin 1 or 4) instead of the battery.
It's also important that the original demo software WILL NOT work, after
this change the source code must be modified and recompiled to ensure the
usage of the DTR line.
I haven't done it myself, I re-write the code in Delphi for using it under
Windoze and to add some features (samples store to file for registration,
etc.) and extra HW (Egely Wheel: http://www.ambro.hu/borze/egely/index.htm)
to one event switch port.
3. I wonder if it's worth to expand the bandwith (low freq. to 1 Hz, maybe
high to 25 Hz), or to change EPROM SW to 9600 Baud transmit rate and to make
some oversampling to 128 samples per sec.
Any ideas?
Regards,
Laszlo Lovass
prochess@elender.hu
PS: I like this HAL kit, simple but great
)