snips.......

Funny, I was just looking through the catalog yesterday, too. 8

channels is not

enough, but you could put a 8 x 2-to-1 " analog multiplexer in front.

But there

goes the neat one-chip solution.
The PIC17C76X with its 16 channel 10-bit A/D would be ideal, but the chip
programmer and socket adapter is prohibitively expensive ($200 + $160).

I didn't see 8 separate analog inputs on the data sheets you uploaded

for the

16F877.

Finn

Keep looking. The rest are down at the bottom port.

An external data selector is no big deal. One additional chip.  Four
control bits will select one of sixteen of course. That gives you a total
of 7 direct and 16 multiplexed for a total of 23 A to D channels with
just four additional control output lines from the PIC. See the
schematic below.

Or of course you could use two PICs for a total of 16 channels.

Paul Lamar

First I made a mistake here. I cannot find a 16 channel analog multiplexer.
Plenty of 8 channel versions. That is not to say they are not out there.

Finn, do you think this cheap ($2.34) 8 pin serial EEPROM is fast enough to
store data for later down load through the 16F877's RS232 serial port
to a PC. I am thinking we could including the data acquisition mode for
very little additional cost with chips like this. Perhaps you can set
up data on a port and let it cook while you go away and do
something else for 5 ms. 8K by 8 will store a lot of data in packed
BCD mode.

BTW forget a single chip solution. PC boards are cheap and quick
with several services offering three day turnaround.

I noticed that the price of the RMI EFIS kit is $1000 for
only about 22 A to D outputs to a rather limited LCD.
Not all at the same time. http://www.rkymtn.com

Looks like there is money to made here :-)>

Paul Lamar

Paul,
I would gleefully welcome a kit of parts (reasonably priced) with
instructions, that I could assemble at home.  It would hopefully include a
printed circuit board, PIC's, multiplexer, LCD, etc.  ...and a some basic
software to get it up and running.  Anyone else interested?
Mark Steitle

I am working on Finn. Unfortunately Finn does not need or like to work.
I know he can do it if we can talk him into getting off the beach.
Tracy is working up something as well. We will just have to wait.

Here is another interesting way of storing a lot of data. This would be the
high end as it cost $27 for the Flash memory chip alone. It would require a several
more low cost chips to interface it to the PIC like an address counter.
This would save a whole bunch of data for a whole flight. Four megabits
or 512K bytes. It would also save the data super fast so the PIC would
not be slowed in its other duties. 45 nano second access time.
The data dump to the ground bound PC through the RS232 interface
should also be faster.

Paul Lamar

I just had a brilliant idea. Data acquisition with no PIC programing
or processor time overhead. Every time you sent a 4 bit BCD digit to
the LCD it could also automatically go to the above flash memory chip. 
Bingo! Real cheap and practical data acquisition. Little or no additional
hardware other than the flash chip and several 50 cent peripheral
chips such as a 4 bit to 8 bit  multiplexer and memory address 
counters which you would need anyway. No additional PIC output 
ports required.

Paul Lamar
 
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