servo signal booster 3.3v -> 5v ?

Forum 2005-2010 (read only) Hardware Interfacing
1

hi there,

i'm using arduino pro mini (8MHz, 3.3V) to control a couple of servos. the servos draw power from an external 5v power source, and the control (PWM) signal is generated from the arduino (using the built-in servo library).

the problem is that the servos exhibit spontaneous twitching (jitter) every several seconds. when i replace the arduino to a 5V version - it solves the problem.

since i need to use the 3.3v version in my project - is there a simple way to boost the control signal up to 5v ? thanks..

ps: googling abit, i came up with this 'logic level converter' from sparkfun (http://www.sparkfun.com/commerce/product_info.php?products_id=8745). how does it work? can i build something like this from scratch? (no time to wait for a delivery...)

2

The simplest way is to use a transistor. This will however invert the signal. If this is undesirable you need two transistors, one after the other.

3

could i use an h-bridge for that?

or something like that: http://www.sparkfun.com/datasheets/IC/uln2803a.pdf

?

4

That is really overkill. It would work but there is no need.

However that data sheet is for a darlington driver not a H-bridge.
That is just like 8 transistors in one package, it will invert the signal just like a transistor.

5

ok. the things is that i need to control 4 servos.. so i'm looking for a 'convenient' solution.

how about something like this - http://www.nxp.com/documents/data_sheet/74LVC125A.pdf ?

6

Yes that will be fine, run the supplies off 3v3 and connect the outputs to the servos.

7

This will however invert the signal.

Surely this depends on the type of transistor you use :stuck_out_tongue:

8

What type of transistor is non inverting?

9

Oh, I get you now... :wink:
The afternoon has only just started, give me a break ;D

10

Any 74HC chip will do, that is non-inverting. You can wire whatever NAND, NOR, AND, OR, INVERTER.... You for sure must have some of them!!

On the other hand you can easily modify the Servo library to output inverted pulses to be re-inverted by the chip....

11

Any 74HC chip will do, that is non-inverting. You can wire whatever NAND, NOR, AND, OR, INVERTER....

how do you mean ?

12

The simplest way is to use a transistor. This will however invert the signal. If this is undesirable you need two transistors, one after the other.

Well, one probably can use a resistor on the emitter side of an NPN transistor and connect the desired output between the transistor emitter and the resistor.

edit:
Per the second interactive circuit in the below page, putting a resistor on the emitter side the voltage still will not be above 2.7v, so my suggetion is NA for this situation.

13

how do you mean ?

sigh
Any 74HC chip with Vdd at 5 V will accept 3.3 volts as HIGH.
So it functions as at fancy transistor.
If you have NANDs, NORs or inverters, you can chain two of them, there are generally 4 in a package...

I proposed that, as you wanted some IMMEDIATE help,,,,,

14

thanks!