Servo Issue With Axon

[Mastermime]

Hello everyone,

This post is also in software (Servo Code), but I figure this particular issue deals with electrical. 

So here is my setup: 12v > Axon II > 12v Pins > L7805 linear regulator > servo

My servo draws 350ma max.  I will be operating at half speed though so the current draw will be less.  I just wanted to confirm that this little circuit will solve my problem.  I know I'll be wasting 2.5-3 watts, but that doesn't really matter to me.

Thanks

Jason

[Soeren]

Hi,

[...] I just wanted to confirm that this little circuit will solve my problem.

What little circuit?

[Mastermime]

Actually it hardly could be considered a circuit.  Those would be the 3 pins on the Axon II.  All I'm doing is placing a regulator between 12v unregulated pin and the servo to drop it down to a voltage the servo can handle.

12v unregulated pin-----------------------LM7805----------Servo

Servo pin-------------------------------------------------------Servo

GND-------------------------------------------------------------Servo

Hope this makes sense
Thanks

[Gertlex]

Presumably the regulator has a ground, too.

[Mastermime]

Oh yeah I forgot to add that in there.

[Soeren]

Hi,

Actually it hardly could be considered a circuit.

Anything with current circulating is a circuit, hence the name

I have attached a schematic of the minimum use of an 7805 that you ca get away with.
Mind you, the excess voltage means that you need a heatsink.
A 10 Ohm 2W resistor between the 12V and the input of the 7805 will gobble up some of the excess power.

If you want to raise the voltage a little, a signal diode (1N4148 or 1N914) in the ground lead of the 7805 (but the caps need to go to ground directly) will raise it to ~5.7V.

[Mastermime]

Thanks a lot for the schematic.  So in American terms I need a 0.22uf non polarized capacitor between input and ground and a polarized capacitor between output and ground?  I'm unfamiliar with that abbreviation 'ut'.  Could you clarify?  Sorry for my ignorance.  Im embarrassed

[waltr]

Thanks a lot for the schematic.  So in American terms I need a 0.22uf non polarized capacitor between input and ground and a polarized capacitor between output and ground?  I'm unfamiliar with that abbreviation 'ut'.  Could you clarify?  Sorry for my ignorance.  Im embarrassed

Seems to be a typo. The cap value would be in uF (microFarads).

220nF = 0.22uF. Both are now used in the US.
This would typically be a ceramic cap.

No need to be embarrassed. Asking questions to get a clarified answer is a good thing.

[Soeren]

Hi,

So in American terms I need a 0.22uf non polarized capacitor between input and ground and a polarized capacitor between output and ground?

Yes.

I'm unfamiliar with that abbreviation 'ut'.  Could you clarify?  Sorry for my ignorance.  Im embarrassed

Perhaps it didn't write it properly to the bitmap, but it was supposed to read 22F+ (plus sign) meaning 22µF or larger (up to about 50µF, whatever might be around).

[Soeren]

Hi,

This would typically be a ceramic cap.

This is the best type, due to the low ESR, but I think it's more common to get polyester caps in that value (from hobbyist shops). That would work fine as well.

[Admin]

As you may already know, the original Axon can't handle more than 10V because that big blue capacitor is rated at 10V. You can just replace it with a higher rated capacitor (and lower mAh), thereby letting you can use the built-in Axon regulator to do what you wanted. No extra circuit needed.

The Axon II can handle up to 20V because I corrected that "mistake". (I didn't think people would use greater than 7.2V batteries when I designed the original in 2007)

The regulator is the same on both, and can handle up to 1.5A. If it overheats, it will throttle back the current automatically.

[Mastermime]

Ok thanks everyone for the help