FREE - RC Heli Optical Tachometer DIY

[DominicD]

I have moved over to C and atmel controllers. atmel are just as cheap and more powerful. And some of them can be programmed with USB.

[HELINHAWAII]

Well, my even simpler mind needs help until you guys get this ironed out. Can anyone point me in the direction of a 2.5K multi-turn pot? I'm really having trouble finding one.

[mikef]

hmm. I'll get the number off my the one I used and see if I can find somewhere that sells them. I just had one on my bench and have no clue where I got it. You can also use one that is close (like a 2k or 3k if they exist).

[HELINHAWAII]

2K are in fact easier to find.

[TheBum]

Originally Posted by HELINHAWAII

2K are in fact easier to find.

Or 5K on the high side.

[HELINHAWAII]

What is the difference in the 2K versus the 5K...besides 3K ohms! Using one would be more sensitive over the other?

[DominicD]

2k is better .... 10 turns divided by 2k or 5k ...... better resolution.....more RPM control.

[fireup]

Originally Posted by HFG

2k is better .... 10 turns divided by 2k or 5k ...... better resolution.....more RPM control.

No, it does not effect resolution if it's 2K or 5K if they are both 10 turn, it just effect the amount of current your circuit will draw (and that is just a little bit). Either 2K or 5K will work, you just have to adjust the trim pot also to get the same range.

[DominicD]

2,000/(10turns * 360 degrees) = 0.555 ohms per degree

5,000/(10 turns * 360 degrees) = 1.388 ohms per degree

The two pots setup a simple voltage divider for the 317 voltage regulator. The more resolution you have the more accurate you can control the voltage to the motor.

[fireup]

Here's the equation for the LM317,

Vout = 1.25V * ( 1 + R2/R1 ) + (Iadj * R2)

R2 is the 10 turn pot and R1 is the 10K trim pot. Yes if you make R1, the same value for both 2K and 5K pot, you'll have different resolution. You will also have different range. But because R1 is also an adjustable pot, you can also increase its value so you get the same range and resolution.

[DominicD]

Fireup all else being equal the 2k has better resolution.... they cost the same so get the 2k

[HELINHAWAII]

That's what I've got in the cart!

[dxtarl]

Originally Posted by HELINHAWAII

Thanks man! I'm kinda dumb regarding this stuff... I'll post a parts listing from DigiKey or something when I get it ordered.

Do you have the parts list yet if sow could you send a copy my way, thanks.

David

[Flatland]

I think this is my first post, so hello all. Been a long time reader.

We used PICs in my EE senior design course in our autonomous UAV. The higher end models are plenty capable little processors. Anyway, to even further drive down the cost of this project, Microchip will send out FREE PICs as samples. Yeah, they only cost a few bucks anyway, but free is even cheaper. I think you can sample four different types of PICs and up to three of each type (so 12 PICs total) every few months. Shipping and all.

Also, there are USB programmers for PICs. Those serial ones are just the old school way of doing it. Our UAV was sponsored by Mikroelektronika and their programmer, MikroC, is really easy to use. They have libraries already built for just about everything the PICs can do with hardware, and even software emulated stuff, too. Plus they make a ton of useful test boards and programmers.

[mikef]

Fireup is right about the 5k, it will work just fine for this project. Any thing around those values will work because you can adjust the small trim pot to make up for it. I used a 2.5K linear pot because that’s what I had in my junk box and I did not know they are a pain to buy. Also, Rond swapped out the 9v battery for a small lipo battery. I think it is a 2 cell pack but you will have to ask him to be sure. It saved on space and it holds a charge forever (so I'm told)

I'll add all these tips to the write-up so others will not have to do this all over again. If someone manages to get a real parts list I would gladly add it as well.

Mike

[HELINHAWAII]

Alright fellas...parts list attached!

I went with www.futurlec.com for the switches, project box, knob, LCD and experimenters board. Total- $15.10

For the rest of the electronic components, www.newark.com has everything in stock and doesn't charge a handling fee like Digikey. Total- $18.17

There are less expensive components for the job but I chose the ones that had better mounting potential and were a little more pleasing to my eyes...like a blue LCD w/ backlighting and blue buttons . Feel free to substitute.

Also, I plan to use the DC motor from an old screwed up HS81 servo. It's pretty small an makes plenty of power for a shutter disk.

And ENJOY!

UPDATE: Enter coupon code "PB15" for 15% off your order @ www.newark.com

[jared_of_atlanta]

Thanks for the shopping list!

[DominicD]

Flatland you misunderstood my USB programming post. Yes there are USB based programmers but you still have to BUY a usb programmer which start at around $100. The Atmel can be programmed directly with the USB connection without the requirement of a special USB programmer. Kind of silly to buy a $100 programmer for a $10-20 project.

[TheBum]

The Newark shopping cart file just endlessly reloads. How do I get it to load once and stop?

[DominicD]

Go to digikey.com ?