Servo Amp Meter (led!)

[hoveratom]

Hi all. I sucessfully made a servo amp meter using ICs and LEDs. Here are the schematics.

It does work. Your servos glitch more than you think!! Some to 1/2 amp. anyways. If you have ideas on how to better this circuit. Let me know.

tom

[dleroi]

Clever!

[rc404]

Very nice. I had thought about something like this with an LM3914 but was wondering how to do the current sense (other than just a resistor). Can you tell me what the two capacitors accomplish and how you choose those values.

The other thought I had had was to combine something like this with a simple servo cycler (AVR/PIC) to look at the current when the motor is at constant speed. To try to look at the effect of linkage binding rather than just at startup transients.

Ed

[Acetronics]

Hi, Hover

I was wondering about the effect of your .39 Ohm resistor ...

drawing 1 amp reduces the servo voltage of ... .39v ( ha,ha ! I'm sooooo clever !!! ) and that is not the current drawn for your batt voltage !!!

Those motors current draw really changes for such a voltage change ...

Alain

[hoveratom]

I choose the caps because the 1000 tends to take the spikes out. I guess servos have HUGE voltage spikes!! It seems to work a little. I attached the smaller cap just to filter out higher frequency noise. I didn't have a 020 so I used something close. it runs fine without the caps across the .39 resistor.

Oh. RUn it with a full battery pack. you can ever use a 5 cell battery if your worried about the voltage loss. remember this is just a cheap fun thing to see how much your servos spike!! Do not fly with this thing attached!! I better add this to the schems.

[hoveratom]

I changed the words and added R56 back in. It was set to zero ohms when I checked it. So I left it out before. It might be needed when messing with smaller servos. (lower ref). anyways. Here's V1.2.

[hoveratom]

I use 4 cell battery. with 5 cell you might have to mess with it. I might even try a .2 resistor for the drop. then full scale will be 2 amp. that will make it better for my gas helicopters. using a 5 cell battery and five big servos and gyro. it seems to peak 1 amp a lot!!

I guess I need to make two..


tom

[mem]

Do not fly with this thing attached!! Tom, if you just use this on the bench then is there an advantage to the circuit over simply using an oscilloscope across the .39 ohm resistor? Assuming of course that one has a scope.

[hoveratom]

making a power supply and then using this as a vertical current meter, like a thermometer. I guess that would be cool. I need to make a volt meter now!


tom

[hoveratom]

that a .22 resistor for R1 seems to work the best for gas helicopters. that is a full working system. That means when R1 is .22 ohms. Every LED will be lit if I put a 2 amp load where it says servos.

yae.

[hoveratom]

Seems that certain batteries can only hold certain currents. It seems to be 1C. I only tries a couple packs. but this seems to be true.

So 1000mah battery seems to max out at 1 amp. 1600mah & 1.6 amps. . ..

tom

[hoveratom]

The two packs are nickle metal hydrides. nicads may be different.

[hoveratom]

ok. final update.

I changed the words for the .22 resistor.

also found that you don't need R1 to handle that many watts. I found a 2 watt was enough!!

ok ok..


tom

[waynerr]

Hi Tom,

I am between novice and intermediate in electronics. I have not used the LM339 before. How would I adjust R56 for 2 Amp use, or would I leave it at zero as for 1 Amp ? I don't think so.

I have never heard of an "IPS" motor. Could you explain that, Please ? I Believe if I saw the letters spelled out in full I would recognize it.

A little more novice than intermediate. :o

Thank You So Much,

Wayne

[dleroi]

How would I adjust R56 for 2 Amp use, or would I leave it at zero as for 1 Amp ?

I have never heard of an "IPS" motor. Could you explain that, Please ?

Wayne,

It seems to me (Tom, correct me if I'm wrong) that to make this a 2 amp meter with the same number of LEDs, you would simply add another 0.39 ohm resistor in parallel with R1.

I think IPS stands for "Indoor Power System" and I think Tom is suggesting it for testing because its current draw is within the range of this circuit (again, correct me if I'm wrong).

[waynerr]

Thank You for your input Don.

Tom hasn't had any thing to add ?

Your idea about doubling up in parallel of R1s of .39 makes sense to me. It comes to a 'close' approximation of the .22 Tom suggested for 2 Amp operation, equaling .195 ohms. when paralleled.

I have ordered a few of .39 both and .22. I will try them both. It will be interesting.

Thank You Again Don,

Wayne

[hoveratom]

Hey Don. Your right on the .39's just double up.

You can put a switch in there too. So You can have 1 and and then 2 amp.


Tom

[hoveratom]

circuit is just for toying around! Nothin too serious. It does work. I think over 2 amps, things could get critical. like hot board. burned finger. haa...

Remember, if you use a higher voltage, you need a 7805 regulator. to run the circuit. then you could test your small flight motors.

see,


otm

[waynerr]

Thank You Tom for confirming the idea of doubling up. I got the parts in the other day and will work with them over the weekend. The idea of a switch is such a simple one, but when you didn't think of it, it seems so huge. :o

Thank You Again,

Wayne

[hoveratom]

idea for how to use this tool. is to apply a 1 Amp load or so across your receiver batt. you could put this load on the board. plug it in. then you can see what your radio does under load.

tom