8051 reset problem

[SEB]

Hello,

I have a circuit for an 8051 type microprocessor which executes a 1 minute
program and then shuts down completely. I would like to then have a touch
switch which resets the power supply to begin execution again. I find that
cutting the power supply and then re-connecting the power supply works, but
I need to cut the power supply for about 30 seconds before it will reset.

Since I want the battery to last a long time (e.g. a year or more), I would
like to take this shutdown approach rather than an interrupt approach. But,
I would also like to use a touch switch to reset rather than a hard off/on
toggle switch.

Any suggestions?

Many thanks

 

[Andrew Holme]

Hello,

I have a circuit for an 8051 type microprocessor which executes a 1
minute program and then shuts down completely. I would like to then
have a touch switch which resets the power supply to begin execution
again. I find that cutting the power supply and then re-connecting
the power supply works, but I need to cut the power supply for about
30 seconds before it will reset.

Since I want the battery to last a long time (e.g. a year or more), I
would like to take this shutdown approach rather than an interrupt
approach. But, I would also like to use a touch switch to reset
rather than a hard off/on toggle switch.

Any suggestions?

Many thanks

30 seconds? That's a long recovery time.

You shouldn't need to interrupt the power supply.

Doesn't your processor have a reset pin? Can't you wire a push button into
the power-on reset circuit?

The reset signal is often taken from the junction of a resistor and
capacitor, connected in series across the power supply. The manual reset
button is then connected across the capacitor.

 

[peterken]

Hello,

I have a circuit for an 8051 type microprocessor which executes a 1 minute
program and then shuts down completely. I would like to then have a touch
switch which resets the power supply to begin execution again. I find that
cutting the power supply and then re-connecting the power supply works, but
I need to cut the power supply for about 30 seconds before it will reset.

Since I want the battery to last a long time (e.g. a year or more), I would
like to take this shutdown approach rather than an interrupt approach. But,
I would also like to use a touch switch to reset rather than a hard off/on
toggle switch.

Any suggestions?

Many thanks

try using a SR-flipflop of the 4xxx C-mos series (eg 4013)
these use only uW of power if static
use the output to control a transistor that switches on the power line
have the reset controlled by the 8051
have the set floating or weak-preset towards the touch switch
(don't forget clamping of the "floating input" to avoid damage! )

 

[SEB]

Thank you for the answers, guys! I have enough to proceed.