Cleaning up power spikes with servo's

[Marcwolf]

I am wondering how other have handled a situation where one had to use a fairly powerful servo on the same line as a Picaxe, and one needs to ensure that the Picaxe is isolated from spikes and other power issues.

Having just blown a 08M because the servo was creating too much noise on the power line I am looking for solutions :>

I would like to use a dual power system but cannot.. So I am running my servo at 5V.. Same as the Picaxe.

Many thanks for any advice

Dave

 

[papaof2]

6 volt supply for the servo, plus a 5 volt low dropout regulator for the PICAXE?

John

 

[wojeepster]

time for a protection diode. 1n4001 across the servo leads bar on diode on the + side. (This is reverse of normal current flow and only comes into use when servo is turned off and makes a spark as the magnetic field breaks down) Use the same deal on relays, bar on diode pointed to the +

 

[boriz]

Yep, also…

A 220uF electrolytic and a 100nF cap in parallel across the Picaxe supply pins, as close to the Picaxe physical pins as is practical.

 

[MFB]

For this type of application, the only real way to be sure of protecting the PICAXE from noise spikes is to use a separate supply and opto-isolators on the I/O lines. The separate supply could be an isolated DC-DC converter powered from the motor supply. These converters are now getting almost as cheap as a collection of linear regulator parts and much more convenient.

 

[BeanieBots]

Your servo "blew up a PICAXE"
What sort of servo is this?
They are designed to work with sensitive radio equipement providing the control signals. They don't produce power supply spikes in the same manner as a simple motor. What thay can easily do is bring down the power supply when they start and pull several amps. A 7805 regulator cannot supply enough current for even a small servo starting up.
Whatever you have supplying power must do so via seperate regulators, one for the PICAXE and one for the servos.
Don't forget all the required decoupling caps.

 

[InvaderZim]

It would help to fork both your power and ground wires at the supply, to make sure the current to the servo is as separate as possible from the logic lines. Also, beef up the bulk capacitance near both the logic side and the servo, and use bypass caps (0.1uF parts, or a mix of 0.1 and 0.01uF).

 

[Wrenow]

Dave You might find it easier to start with a known solution like the AXE 024 http://194.201.138.187/epages/Store.storefront/?ObjectPath=/Shops/Store.TechSupplies/Products/AXE024
either as a base for a servo project or at least for a schematic for how to hook it all up for protection (notice the 3 filtering caps and where located, as well as the voltage drop and protection diode). Of course, starting with a proven design, the circuit board already made up and parts determined and picked, saves a ton of time. This little jewel is the basis of many of my servo based projects, and, in fact, is my default starting point. And, yes, the inputs are available on the board.

Cheers,

Wreno