John Fields said:
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Check alt.binaries.schematics.electronic in a little while for a
discrete CMOS solution.
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Assuming 1mA max for each chip for the CMOS solution, you'll need 21
HC14's, 17 HC165's, 3 HC160's, 3 HC4511's, and 1 HC40103, for a total
of 45mA for the logic.
Power issues for your sensor array? Who knows? You haven't pasted
anything at all about that in terms of what your sensors are, how much
power they consume, what tour power supplies look like, etc...
John,
Thank you for posting a schematic, it was useful to see the ideas
being discussed in a diagram. After further consideration (I've
described another possible design in another post), I'm resolved to
the fact that there is no real clean plain-part ttl or cmos solution.
There are simply too many sensors.
In a last attempt to try to reduce the count, I have been toying with
the idea of an xy grid representation of sensors using schmitt
transceiver with tristate output. I haven't fully analysed whether or
not it will work but the gyst of the idea is this:
xy grid of sensor inputs whose row/cols are terminated by schmitt bus
transceivers. Transceivers are enabled via decoders in sequence, their
output is piped via mux or shift registers (with a seperate clock and
some logic) to an AND gate. So, sequentially, every strobed xy point's
output is sent to the AND gate (one from the x-row, one from the
y-col), which, in turn, is finally piped into the chained 7490s
controlling the count. Hope I've explained it clearly enough.
This design seems to cut the chip requirements by about half, however,
this is still not the most novel or extensible solution. I'm
considering CPLD solutions now. Any advice on this front would also be
much appreciated. At the moment I'm researching solutions from Xilinx
but not fully clear about what a beginner kit would be. It seems that
I should simply pick any CPLD that fits my current/future
pin/macrocell requirements, buy the demo board offered on the site,
use their free WebISP software, and use my VHDL book
When I asked about power requirements on the sensors, I should have
been more specific, I was prompting for more advice on pitfalls I
should expect rather than specific issues. My sensors are simple
photodiodes with a resistor, my choice for photodiodes was completely
controlled by their relatively-to CdS and Phototransistors-cheap
price. I was wondering what I should keep in mind when dealing with so
many sensors spread out over such a large surface - resistance in long
wires, capacitance issues, speed issues, mechanical considerations,
designs which lead to unrealistic power supply expectations, other
electrophysical problems, etc.
Thank you for your help and advice! (that goes for everyone who posted
Avital