> Im trying to figure out a way to use the 16F84 to detect if a voltage is above of below a
> certain level, the PIC will be powered from a separate >source (I hope)
> If the voltage hits a certain level the PIC will switch the surrounding devices on
> just to be difficult when the voltage is equal to or below the required level the
> circuit must not consume power
> The power supplied to the pic comes from a 1F supercap and needs to be replenished by the
main supply, there also may be a lithium battery available for standby.
>
> Any ideas as to how to do this?, or is this a little beyond the 16F84....
> also I would like to expand the available I/O lines in some way so I can have
> more sensors and outputs available, IM guessing I can use a standard
> MUX/DEMUX to do this, or would I be better off using a second 16F84.
>
Sounds like you have an SLA battery that you need to
protect.
I used a 12C672 to do this( A/D ports) but there is no
reason a 16F84 cant manage this.
The main thing to work out is how to detect analog levels
with digital pin/s.
The good old cheap and simple hardware (but adding
software) method , as well documented by Microchip, is
to time the charging of a cap, the time being proportional
to the voltage and then short out the cap just before you
perform another reading.
This also has the benefit of drawing no significant current
if not being read.
This measured voltage is now compared in software with
youre desired limits.
To increase the i/o (well output anyway) you could use a
shift register, one with 2 clks where the output is not
asserted until the output clk is asserted... as in a
74HC595.
I built a project that cascaded 3 of these 595's, three
16F84 i/o lines became 24 outputs.
I have circuit diagrams (schematics) and code if anyone
is interested.
In the case of i/o I would gravitate to another pic working
as a slave (say a cheap 16C5x).
_____________________________
Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand
> To increase the i/o (well output anyway) you could use a
> shift register, one with 2 clks where the output is not
> asserted until the output clk is asserted... as in a
> 74HC595.
> I built a project that cascaded 3 of these 595's, three
> 16F84 i/o lines became 24 outputs.
> I have circuit diagrams (schematics) and code if anyone
> is interested.
I would be very interested in seeing your code and schematics if you
have them handy. I am planning to do something somewhat similar, and
seeing some examples couldn't hurt :)
> In the case of i/o I would gravitate to another pic working
> as a slave (say a cheap 16C5x).
Microchip has an application note to do just this. AN541 - Using
PIC16C5x as a Smart IIC Peripheral. I am considering this as an
alternative to many shift register/latches like the 595. My hope is that
I can locate the second pic farther away from the controlling pic with
less problems. I haven't had much time to actually read it though.
> Hi All,
>
> Im trying to figure out a way to use the 16F84 to detect if a voltage is above of below a certain level, the PIC will be powered from a separate source (I hope)
> and if the voltage is below the trigger level it will go into watchdog mode and
> wakes every so often to check the voltage, or if there is a change in the
> environment it will wake and check the voltage.
>
> If the voltage hits a certain level the PIC will switch the surrounding devices on
> just to be difficult when the voltage is equal to or below the required level the
> circuit must not consume power (other than the power supplied to the pic by a separate source).
>
For trigger level I would use a low power consumption
comparator ( biased from one pic pin or not). But all depends on the
signal level you have there.
> The power supplied to the pic comes from a 1F supercap and needs to be replenished by the main supply, there also may be a lithium battery available for standby.
1F it's a little big... (like my room perhaps...) maybe .68 to 4uF
depens on consumption...
> Any ideas as to how to do this?, or is this a little beyond the 16F84....
> also I would like to expand the available I/O lines in some way
so I can have
> more sensors and outputs available, IM guessing I can use a standard
> MUX/DEMUX to do this, or would I be better off using a second 16F84.
No way, 2X84 = 877 (in $) so use a 87x and same effort for code
<x-rich><color><param>0100,0100,0100</param>On 4 May 00, at 23:42, Josh Koffman wrote:
<color><param>7F00,0000,0000</param>> > 74HC595.
> I would be very interested in seeing your code and schematics if you
> have them handy. I am planning to do something somewhat similar, and
> seeing some examples couldn't hurt :)
>
</color> Josh, something similar you can find in JAL (pascal compiler)
distribution; a library called cio.jal at: <underline><color><param>0000,8000,0000</param>http://come.to/jal
</underline><color><param>0000,0000,0000</param>who manage almost any register chip to interface with x84.<color><param>0000,8000,0000</param>
> > > 74HC595.
>
> > I would be very interested in seeing your code and schematics if you
> > have them handy. I am planning to do something somewhat similar, and
> > seeing some examples couldn't hurt :)
> >
> Josh, something similar you can find in JAL (pascal compiler) distribution; a library called cio.jal at: http://come.to/jal
> who manage almost any register chip to interface with x84.
> Vasile
Thank you...now if only I understood JAL :) It's not a big deal though,
I am pretty sure I can do this on my own, I was just curious to see some
examples.
mb.sympatico.ca
