8051 On/Off Circuit

Okay, reverse battery protection added, and also a variation on G1 so that the SW can latch it on but loses control on turning it off, leaving that to the OFF input. The transistor allows OFF to be controlled by low voltage logic signals. View in a fixed-width font such as Courier.

. . . . BATT . CD4093 | . --------- | . .-|gnd Vdd|-------------|--. . | --------- | | . --- |- | . /// .-----|| | . | |< | . | | | . |PMOS SW +--' . QUAD NAND SCHMITT | | . | |< . .---+-------------------------------+-----|| . | | | |- . | | | | . [10k] | __ G1 | '--> TO LOAD . | '_| \\ __ G2| . | | o----+------+-------| \\ | . +-----|__/ | | | o-' . | | | .-|__/ . | | [100k] | __ . | [1M] | | / |------. . | | | '-o | | . | | | | \\__|-. | . | --- | | G3 | | . '---o o------+--------------------' | . | | | . NO SW === | __ G4 | . |0.1U | .--| \\ | . -+- +-----| | o-----' . /// | '--|__/ . | . |/ . OFF>--[10K]---+----|PN3904 . | |>

. [10K] | . | | . '------+ . | . -+- . /// . . .

[.... old version removed ....]

I'm going to modify your circuit slightly. Look for ***

*** The PMOS only needs its gate to ground. There is no need to take away its gate drive when the power is off. This prevents the power of the CD4093 from being a diode drop lower than the Vin when power is off. Although this is a lot less than the Vth of the MOSFET, I would still expect less leakage like this.

This saves the schottky diode in my suggested version.

You can do it with a 8051 CMOS version, I've done it. Still in production. This one has to stomach intermittent power at the end of a long line. During analog processing it's also sent to sleep via PCON for radio silence, then something tugs on a port pin when it is needed for processing. Works like a champ. Best of all these things are 2nd sourced and you can always find local guys wielding a Keil Compiler.

In general I would not trust any RC reset scheme, whether they mention it in the datasheet or not. If in doubt roll your own.

--
Regards, Joerg

http://www.analogconsultants.com/

We've got a new rule - no "Use a PIC" posts allowed without a schematic and full code listing. ;-)

Cheers! Rich

If your uP has a decent "sleep" mode, you could do it with one button. You'd need to blank the LCD, or just shut down power to the peripherals.

Cheers! Rich

Nah, Speed up your PIC, by downgrading to an 8048,

martin

or perhaps not:

Hide quoted text -

Wow. Have to file that one away for future reference. (LCD Contents stable without applied power.)

This particular project would not benefit from no-power LCD display however....

Thanks for the link. Oh, and Happy New Years everyone!!

-mpm

"MooseFET" schreef in bericht news: snipped-for-privacy@z26g2000pre.googlegroups.com... On Dec 29, 12:08 pm, "petrus bitbyter" wrote: [....]

I think you wanted a PNP as the pass device. As drawn it doesn't work. (org. drawing)

I also think you may need a pull up on the processor pin. The 8051s don't pull up very well. Modified:

You're right.

petrus bitbyter

It doesn't apply here. The OP is already using a micro, it is assumed, that they can write their own code. Anyway, I am exempt from that rule. ;-)