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First Robot: Sound + Servo!?


So I'm trying to adapt my robot to make a wake up robot, that makes an alarm, and as soon as the alarm starts, he starts driving so u have to get up to shut him off.

I've put all my components (Battery holder, print board, speaker, motors and sensor) on a Lego base board, and changed the resistor array by the Darlington to make a louder sound. Now today I wanted to add my servo to my front wheels (just & double Lego wheel now), to make turning more comfortable. But it just doesn't want to work. It's really impossible to add the servo without the resistor array? I replaced it by the Darlington, it works, but then my alarm sound is really silent, not really something that can be heard while asleep. So the Darlington is really necessary.

So my question: Is it impossible to get an active servo without the resistor array chip? Do I need a second print board? (please say no :P)

Thanks in advance


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Do you have a schematic to share perhaps? I could probably give you an answer right away but there's not enough information in your post :)

Can it be that your batteries do not deliver enough amps to drive both the servo and the speaker?

Have just finished the Bøsewicht. This robot had (in one development-stage) sound and two servos controlled by the same microcontroller and power-source. So it is possible to combine sound and servo.

It is possible that the batteries can't deliver enough amps. I'm using 4x1.2V batteries, each stating to deliver 'standard charge 245 mA for 16h', would that be enough? The speaker is a 3 ohm one (max 9W), so that would require like 1.6A already hmm...

But the servo isn't working while the speaker isn't making any sound either and the speaker is making a very quiet sound, even while the servo isn't active (with the resistor array chip installed instead of the Darlington).

With the so called 'Darlington' installed, the speaker works normally, but the servo doesn't do anything at all, even when the output of the speaker is low. There shouldn't be anything wrong with the connections, because I used the exact same ones (except for the SHARP sensor, which is on analogue input 3 instead of 0, but kind of irrelevant ^^ ) for the servo, and the speaker is just 0V and +5V wires, they are both working individually (with the correct chips installed though), so I'm not sure what's causing the problem.


Without having a clear idea of what equipment you are using this is kind of a guess based off of your description. It sounds like this "lego base board" can use either a resistor array or a darlington array, not both at once; much like a PICAXE 28 Project Board.

If this is the case, you won't ever get the servo to work with the darlington installed. You don't need the resistor chip to get a servo to work, per se, but you can't run the servo signal through a darlington transistor. The resistor isn't necessary but it stops the uC from being fried in case of a short or some sort of overvoltage. It's a protection device, in short.

If you want the speaker driven by the darlington you need to wire your servo into the circuit before the darlington.

Hm, I think I made a mistake by mentioning Lego base board. I meant I just used Pattex to glue everything on a Lego plate, not really something Lego-electronics :) I'm using everything from the First Robot Starter Kit, including the picaxe 28x1 project board and just glued it on something like this http://upload.wikimedia.org/wikipedia/commons/1/15/Green_Lego_Baseplate.jpg

"If this is the case, you won't ever get the servo to work with the darlington installed" Oke, this made sense to me :) But what do you mean with "you need to wire your servo into the circuit before the darlington"?

Ah, very good then. I reference Frits' 28X Project Board for Dummies post:


The holes labeled "E" and marked in purple are what I'm talking about. They are connections to the PICAXE output pins before they run through either the darlington or 330R array. There's no convenient three-pin connection for instant servo hookups but those are the holes you'll want to connect your servo signal wire to.

Awesome! I connected the white signal wire to the direct output, and both servo and speaker work now (with the Darlington installed)!

Thanks for the help!

Glad to hear it's working :)

Yayy! A clocky type of robot! http://www.nandahome.com/