2

Author Topic: Confused About Axon Pins  (Read 856 times)

0 Members and 1 Guest are viewing this topic.

Offline MastermimeTopic starter

  • Supreme Robot
  • *****
  • Posts: 314
  • Helpful? 5
Confused About Axon Pins
« on: October 28, 2012, 06:19:05 PM »
Hello everyone,

I'm a little confused about how much current the Axon pins can supply.  My question is; Can I activate my relay coil (draws about 150ma) with my Axon?  The supplied voltage to the Axon is 12v.  I understand that input/ output pins can only supply >20ma, but since the row of (battery headers) are interconnected, that shouldn't apply here, correct?

Offline lrmall01

  • Jr. Member
  • **
  • Posts: 38
  • Helpful? 2
Re: Confused About Axon Pins
« Reply #1 on: October 28, 2012, 07:23:06 PM »
I don't think so - you'll need some type of driver between the micro and the relay coil.

Offline Webbot

  • Expert Roboticist
  • Supreme Robot
  • *****
  • Posts: 2,150
  • Helpful? 110
Re: Confused About Axon Pins
« Reply #2 on: October 28, 2012, 08:52:30 PM »
It ain't coming from the battery its the signal pin so its being sourced/drained by the chip! Check the datasheet for ATMega640 - its about 20mA max.
The supplied voltage to the regulator may be 20V - but the supplied voltage to the Axon is 5v (assuming you are talking about an Axon or Axon II).
You 100% need external circuitry to activate the relay
Webbot Home: http://webbot.org.uk/
WebbotLib online docs: http://webbot.org.uk/WebbotLibDocs
If your in the neighbourhood: http://www.hovinghamspa.co.uk

Offline MastermimeTopic starter

  • Supreme Robot
  • *****
  • Posts: 314
  • Helpful? 5
Re: Confused About Axon Pins
« Reply #3 on: October 28, 2012, 10:38:29 PM »
Ok a transistor circuit like this should work, right?
(See image below)

Note: I forgot to put 1k resistors between gate and drain in the schematic
« Last Edit: October 28, 2012, 10:44:38 PM by Mastermime »

Offline lrmall01

  • Jr. Member
  • **
  • Posts: 38
  • Helpful? 2
Re: Confused About Axon Pins
« Reply #4 on: October 29, 2012, 05:54:45 AM »
Your example will work if your relay coil is grounded on the other side.  It is more common to sink the current through the low side of the relay though, also nice to throw in a diode for current to bleed off through once the switch is opened (probably not critical though for a hobby project - this helps with electrical noise caused by the stored energy in the coil).

http://www.pcbheaven.com/wikipages/Transistor_Circuits/

Offline MastermimeTopic starter

  • Supreme Robot
  • *****
  • Posts: 314
  • Helpful? 5
Re: Confused About Axon Pins
« Reply #5 on: October 29, 2012, 11:55:47 AM »
Quote
It is more common to sink the current through the low side of the relay though

I'm not sure what you mean here.  Could you elaborate?

Offline Razor Concepts

  • Supreme Robot
  • *****
  • Posts: 1,856
  • Helpful? 53
Re: Confused About Axon Pins
« Reply #6 on: October 29, 2012, 01:15:41 PM »
Quote
It is more common to sink the current through the low side of the relay though

I'm not sure what you mean here.  Could you elaborate?

Your circuit is "sourcing" current - you are providing a positive voltage, allowing current to flow from the positive to ground.

"sinking" current means providing a connection to the negative voltage, allowing current to flow from the positive (which is already connected to the relay) to the negative voltage (ground)

Offline MastermimeTopic starter

  • Supreme Robot
  • *****
  • Posts: 314
  • Helpful? 5
Re: Confused About Axon Pins
« Reply #7 on: October 29, 2012, 03:00:22 PM »
Ok I think I understand.  I should be applying the concept of electron flow rather than conventional flow.  Could you verify the image to make sure I'm correct

Offline MastermimeTopic starter

  • Supreme Robot
  • *****
  • Posts: 314
  • Helpful? 5
Re: Confused About Axon Pins
« Reply #8 on: October 30, 2012, 01:55:12 PM »
Can somebody confirm that I will be wiring this correctly based on the wiring the image above?

Offline lrmall01

  • Jr. Member
  • **
  • Posts: 38
  • Helpful? 2
Re: Confused About Axon Pins
« Reply #9 on: October 31, 2012, 05:27:12 AM »
Yes - that looks correct.

Here is another reference for you.

http://www.free-circuit.com/2011/05/16/relay-control-with-mosfet-irf511-circuit/

Offline MastermimeTopic starter

  • Supreme Robot
  • *****
  • Posts: 314
  • Helpful? 5
Re: Confused About Axon Pins
« Reply #10 on: October 31, 2012, 08:19:32 AM »
Thanks a lot for your help

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: Confused About Axon Pins
« Reply #11 on: November 02, 2012, 06:47:14 PM »
Hi,

A few things to note...
- A TO-220 MOSFET is way overkill. A BC337 is ample for such.
- Remember a fast diode over the relay coil, or the active element will die screaming.
- The schematic you were pointed to (one of the late Tony VanRoon circuits, stolen from his site BTW), does have a (slow) diode in place, but the resistors at the gate are way too large (always scrutinize his circuits and correct accordingly, he was a really great guy, but unfortunately, several of his circuits are flawed and he didn't get enough time on earth to correct them all).
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

 


Get Your Ad Here