Relays Or Switches?

ftlum

USA

Asked Sep 2014 — Edited Oct 2014

Hi All.

I'm trying to decide how to best activate a couple things on my robot build (full sized K-9 in my avatar).

I need to turn on a laser pointer. I'm thinking a pico switch would work.
http://www.dimensionengineering.com/products/picoswitch

Is there a more direct solution with the EZ B (I'll be upgrading to v4 soon)?

Also, I need to move a car antenna up and down. This particular antenna requires reversing the polarity to get it to move backwards. A switch that's mechanically activated by a servo arm for one direction and another switch for the other direction would definitely work and I'd just need to control the duration of the switch's activation to control how far the antenna extends.

https://www.servocity.com/html/spdt_miniature_snap-action_mic.html

Would a relay be any better? Reversing the polarity appears to be more challenging for my feeble brain-- the simpler the better!

https://www.servocity.com/html/electronic_pwm_controlled_dual.html This one seems to be able to run things forward and backward, but I'm not sure how it'd work with the EZ B.

thanks in advance

Frank

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JustinRatliff

PRO

USA

#1 Sep 2014

First you want to consider what voltages do these items need?

For laser pointers many of those run on 3 - 5 volts. I have a little laser on my robot now that I power directly from the EZ-B. The positive on the laser goes to the signal/data line on the EZ-B. The ground or negative goes to the ground. I don't need anything else. Then I use a digital on/off control in ARC to controller the laser.

Relays overall are, "ok". I personally would tend to think of relays as either a last resort (force myself to use what I have) or us them for switching higher voltage devices. To drive a (I assume) 12volt automotive antenna (?) I think you might want to consider an h-bridge. That would let you control the DC motor forward and reverse from the EZ-B.

Using a servo to control snap action switches is very doable. That's a popular setup for very big robots that relies on standard R/C controls. My advice would be steer clear of that solution for your robot. I believe you would find a h-bridge motor driver a better solution. This page shows how an h-bridge would work.

For the K9 robot, the antenna are the ears, correct? Why would you not want to spin those with a standard servo?

jstarne1

USA

#2 Sep 2014

Honestly a darlington transistor or mosphet used to trip a relay is your best option. Using a servo to flip a physical switch is a bit of a waste of resources.

bookmaker32

USA

#3 Sep 2014

They have TTL controlled relays very cheap. No need for a transistor. TTL Relay Just use a digital port on the EZ-B. They will handle 120V at 10 A.

Dunning-Kruger

Canada

#4 Sep 2014

@bookmaker... EZB digital port can handle 120V at 10A? I must have read that wrong...

jstarne1

USA

#5 Sep 2014

He linked a relay and board that already has the circuit i mentioned soldered together. The relay can turn 110v on and off , the ezb 4.8 v signal triggers the relay on.

Dunning-Kruger

Canada

#6 Sep 2014

Laser pointers will draw more than 20ma, so they cannot be driven directly off the ezb data pin... You will need a relay or a mosfet... I prefer a 5v low mAh relay that can be driven directly from the EZB data pin...