diy r/c frequency checker part 1

I started looking for a good radio frequency project. It just so happened that at the same time, everyone at work was interested in mini r/c helicopters and things like that. In my googling of everything r/c helicopter page ever, I came across a neat little r/c frequency checker for r/c airplanes. I also just happened to be reading some articles on superhet design. A r/c frequency checker seemed like a neat little project to try to do myself. So I set about starting to think about how I would build such a thing. The first thing that I figured I would need would be the LEDs. The r/c airplane spectrum starts at 72Mhz and each channel is 20Khz wide. All in all for airplanes there is a total of 50 channels so I would need 50 LED’s. I started to look around for a 10×5 LED matrix. My searches turned up nothing. Sure I could get a 8×8 LED Matrix and just not use the extra 14 leds but I didn’t think it would look as cool. So I set out to design my own. It seemed that If I designed mine so that it was just the LEDs and some pins on one board and all the control circuits on another board then I could re-use my LED matrix just like if I had bought one.

The way LED matrices work is all the anodes of a column are connected and all the cathodes of a row are connected. See the schematic below. 
10x5 LED Matrix
When you see the layout of the PCB you’ll see why I have the extra pins for the rows. Anyway when you want to display a certain set of LEDS you scan through each column enabling one column at a time and while each column is on you enable the correct rows corresponding to the LED you want on. If you cycle through all of the columns fast enough the eye thinks all the LEDs are really on at the same time.

I took this time to also teach myself EagleCAD since it’s free and there seem to be a lot of good tutorials on it. So I decided for the PCB that I would layout all the LEDS on one side and then put some breakway headers on the bottom side. This would then let me design a second board with female headers and all the LED controlling circuitry and RF circuitry on it.  
10x5 LED Matrix PCB
I decided to keep all 10 pins for the rows even though I only have 5 rows just for stability when plugging into the second board. Overall I found EagleCAD easy to use. The schematic was really easy to draw up after getting the controls down. The PCB took a little more time but I think for my first attempt at a custom PCB it came out okay.

The real reason for this post is that I just got my custom PCBs in the mail and I wanted to share pictures. 
pcb front and back
I ordered 1 copy but ended up with 4 which was even better. The picture above is two of the PCBs one showing the front of the board and the other showing the back. Anyway check back for more posts as I assemble the LED matrix and the second board with all the controlling circuitry. 

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Posted on March 31, 2008, in Electronics and tagged , , . Bookmark the permalink. 8 Comments.

  1. dokumentamarble


  2. I do video production, and when we use wireless mics we are often struggling to find free radio space to operate. Do you think your project would be adaptable to that application? I don’t know how many frequencies there are available, but it seems like the same problem we’re facing.


  3. I would think that this probject would be adaptable to wireless mics. The R/C stuff is in the 72Mhz range. A quick google search tells me that wireless mics are somewhere up in the 170Mhz range? The frequencies you check are absed on the superhet circuit that will be on the second board. superhet’s work by translating the real frequency you’re interested in down to an intermediate frequency that is easier to work with. It seems to me that it would probally be asy to modify the part of the superhet circuit that controls which frequency range you’re looking at. Of course I have no idea ho wide the channels or how many channels there are so I don’t know if 50 LEDs is helpful for wireless mics or not

  4. Who did you use to produce the PCBs?

  5. I ordered the PCB through it took about three weeks. But I ended up with 4 copies instead of 1 so It worked out good for me

  6. Jonathan Herr

    Sounds like a pretty good project idea, and your blog seems interesting, but those ‘’ website preview things are a bit annoying. Is there any way you could remove them from this blog?

  7. I’m doing a project right now that needs to have a fast frequency checker (faster than 15sec for sure). How is your project going? are you done? I would love to see how it turned out or if you have some ideas for a good schematic.

  1. Pingback: PCB milling hell sunday extra - Hack a Day

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