TheBackShed.com

Forum Index : Microcontroller and PC projects : Supervisory and manual reset

Author

Message

MicroBlocks

Guru

Joined: 12/05/2012
Location: Thailand
Posts: 2209

Posted: 05:29pm 03 Oct 2015

Copy link to clipboard

Print this post

I made this variation of using a supervisory chip to provide a clean reset signal to the microcontroller.
This would eliminate any debounce when a switch is used for a manual reset. There would be no need for a R/C type debounce which could also interfere with programming a chip. I think this would be the cleanest way of having a reset signal.
I have protytyped it and it works good.
Any remarks on the schematic? Did i overlook something?
The chip has an operating current of around 45 microAmps and it trips with voltages lower then 3.0-3.15v

I would like to make this a standard part of any module that has an mcu.
Edited by MicroBlocks 2015-10-05

Microblocks. Build with logic.

Grogster

Admin Group

Joined: 31/12/2012
Location: New Zealand
Posts: 9066

Posted: 05:41pm 03 Oct 2015

Copy link to clipboard

Print this post

Nice and simple, and looks OK to me.
This is an effective design, as pressing RESET will pull pin2 of the 130 IC to about 1.65v or so, thus tricking it into forcing a CLEAN reset state - clever.

Smoke makes things work. When the smoke gets out, it stops!

MicroBlocks

Guru

Joined: 12/05/2012
Location: Thailand
Posts: 2209

Posted: 05:52pm 03 Oct 2015

Copy link to clipboard

Print this post

My concern is the values of the resistors.
R1 will effectively make the treshold of the supervisory chip higher by 330x45uA = 14.85mv. So it will trip when the power supply is between 314.85 and 329.85.
That might be a bit to close to the 3.3v. A 100 ohm resistor for R1 will add only about 5 mv.
I also not want to much current to flow when the reset switch is pressed.
When using 100 ohm for both resistors the current is 3.3v/200 = 16.5mA. Way to much.
3.3v/660 will be only 5mA.

Maybe the best compromise is 100 ohm for R1 and 330 for R2.....

Practicing my Ohm's law calculations. :) With all the digital stuff it doesn't get the attention it deserves.

Edited by MicroBlocks 2015-10-05

Microblocks. Build with logic.

MicroBlocks

Guru

Joined: 12/05/2012
Location: Thailand
Posts: 2209

Posted: 09:15pm 03 Oct 2015

Copy link to clipboard

Print this post

I just realized that i could just use a MCP130 that triggers on a lower voltage to compensate for the 330 ohm resistor.
I tested it with a MCP130-315 but without a variable power supply i did not test how it responds to little voltage dips.
I can replace it with 1 MCP130-300 which has a trip voltage of 2.85-3.00.

Microblocks. Build with logic.

Chris Roper
Senior Member

Joined: 19/05/2015
Location: South Africa
Posts: 280

Posted: 10:38pm 03 Oct 2015

Copy link to clipboard

Print this post

Won't this be a problem in Battery Operated applications ?

At 2.85 Volts your battery's still have life left and the PIC32MX can operate down to 2.3 Volts.

Just a heads up for low power battery applications.

Cheers
Chris

http://caroper.blogspot.com/

MicroBlocks

Guru

Joined: 12/05/2012
Location: Thailand
Posts: 2209

Posted: 02:56am 04 Oct 2015

Copy link to clipboard

Print this post

The PIC32 can operate ok at those voltages, most other parts that are controlled by the mcu not so much.
When batteries are used it is best to either leave out the supervisory chip or up convert to 3.3v

Microblocks. Build with logic.

Print this page

To reply to this topic, you need to log in.