Hello Greg.

31 Aug 04 08:57, you wrote to Roy J. Tellason:

 GM>  -=> Roy J. Tellason said to Greg Mayman
 GM>  -=> about "UNKNOWN IC" on 08-26-04  12:06.....

 RJT>> And that implies software,  and that the chip has some code in
 RJT>> it...

 GM> Almost certainly these days.

 GM> CHANGING THE SUBJECT....

 GM> Does anyone have a circuit of a deep freeze failure alarm? I
 GM> recently had to empty about $60 worth of stuff into the garbage
 GM> when we found the power plug on the freezer had been bumped and
 GM> the thing wasn't working.

here's a simple one.

       .--- themostat --- electric nosise-maker -----.
       |                                             |
       `---------- battery --------------------------'

actually I can't improve on that.... any sort of solid-state sensor in
coing to be a continuous draw on the battery andif you powerit from the
mains some fool may knock the plug out, ot pull the plug to plug something
"more important" in.

 GM> I thought I remembered seeing such a gadget as a project in one
 GM> of our electronics magazines some years ago, but I can't find it
 GM> in any of the copies I've saved.

temperature sensors are easy , thermistors are gettign harder to find but
but the new semiconductor temperture sensors are more stable, and even give
linear response

 GM> I have some ideas of my own, but I thought I'd toss the matter
 GM> into the ring to see whether anyone has already got something.

 GM> The requirements are:

 GM> 1. Battery powered

 GM> 2. Alarm to go off if temperature rises above a preset limit.

 GM> 3. Preset limit to be adjustable between 0 deg C (32 F) and -20 C
 GM>    (-4 F) or thereabouts.

 GM> 4. Long battery life in the non-alarmed condition.

in solid state that's the tricky bit.... I guess a long-cycle bistable
could be used to only power the circuit up once a minute or so.

it's not like there'd bemuch advantage to checking the temperaturein there
more often than once every 5 minutes,

heck if youv'e got the hardware to do it go with the "lightest"
microcontroller you can find and power the sensor (and associated divider
chains, adjustment pot, comparator) off one of the outputs or mosfet driven
by one of the outputs

the other output can drive a piezo noise-maker.

 GM> 5. Alarm to be able to operate for several hours without draining
 GM>    the battery, in case the house is unattended when the alarm
 GM>    goes off. Alarm must be very low drain or operate in short
 GM>    beeps.

Those piezo nosimakers used in smoke alarms etc don't use much power.

if it's a one off: I don't know what you'd pay for a new freezer
thermostat, but a used one can probably be had cheap if you can trust it.
noise makers can be had for free from expired smoke alarms.

not looking for a place on "new inventors" are you?

Jasen

--- GoldED+/LNX 1.1.4.7