Author Topic: how to turn off my robot automatically?  (Read 1050 times)

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Offline ibotTopic starter

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how to turn off my robot automatically?
« on: April 27, 2010, 03:52:33 PM »
I was really wondering how to turn off my circuit automatically?

Currently, my robot is keep on going until I take the power off manually by pulling the +ve and -ve battery wires from circuit.  Now, .. I want my robot to completely shutdown when it finds an object in its path or something like that. Is this something I can control from a microcontroller ? are there any other possible ways ? probably, this might be a famous question. If you can redirect me to some helpful links, that would be great too.

Greatly appreciate any help !! Thanks !!

Offline Soeren

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Re: how to turn off my robot automatically?
« Reply #1 on: April 27, 2010, 04:00:33 PM »
Hi,

[...] Now, .. I want my robot to completely shutdown when it finds an object in its path or something like that. Is this something I can control from a microcontroller ?
Yes, let a transistor switch the current.
Hold the base through an output pin (via a resistor or two) and to start, let a switch bypass the transistor.
(Do you need a schematic for that?)

That expects the rest of the circuitry to be disabled with the controller. If that's not the case, a relay can be used.
Please post max. current draw of the line(s) that you want switched off, if you need a schematic.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Admin

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Re: how to turn off my robot automatically?
« Reply #2 on: April 29, 2010, 10:19:35 AM »
The transistor idea won't work, as when the microcontroller turns off, who knows what will happen to the gait of the transistor. Worse yet, how do you turn it back on?

The correct way would be using a hard switch. Attach a servo to a physical on/off switch, and have your microcontroller use the servo to kill power. Just make sure you design it so the switch is fully off before the servo doesn't have enough power to move it. You may need to debounce the switch (google how to do it).

Offline Soeren

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Re: how to turn off my robot automatically?
« Reply #3 on: April 29, 2010, 01:28:42 PM »
Hi,

The transistor idea won't work, as when the microcontroller turns off, who knows what will happen to the gait of the transistor. Worse yet, how do you turn it back on?

It works just fine and have been for numerous years. Turning it on, as I wrote "to start, let a switch bypass the transistor."
The gate (or rather the base, as a BjT is best used), is of course held at a known potential at all times.


See the attached circuit.

Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline dunk

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Re: how to turn off my robot automatically?
« Reply #4 on: April 29, 2010, 03:06:22 PM »
there are power management ICs that drive MOSFETs for this purpose if you don't have a microcontroller on your project.
i've never bothered using one though.

as Soeren says, if you have a microcontroller on board just drive the MOSFET using that. a pullup resistor to keeps the state while the microcontroller is powered down.

another option i used before i knew enough about MOSFETs, some voltage regulators have an enable pin. eg. LM2574.
with one of these you can power down the regulator from your microcontroller.
i can't remember if you need a pullup resistor or not... the regulator datasheet would tell you.
a simple push to make switch pulling the regulator enable pin to ground allows you to switch it on again.


dunk.

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Re: how to turn off my robot automatically?
« Reply #5 on: April 29, 2010, 08:56:49 PM »
Interesting . . . I stand corrected.

That said, the servo idea is 100% efficient, as the transistor method will burn a percentage of the power as heat. :P

Also for high power situations a relay will work great, but again it will waste some amount of energy to activate.

(it really depends on your system and your design limitations)

 


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