Working with 8 bit gray code and Prop 1
AGCB
Posts: 327
in Propeller 1
I have an 8-bit absolute encoder that I'd like to use with a wind direction indicator. Does Propeller 1 know about gray code 
. My previous try used a total of 8 magnet/switches to get 16 8-bit hex outputs. I'm not sure how to start with this or if I wasted my money. Help
Aaron
Comments
Well, you do not tell too much here.
I would read the 8 bits and then perhaps use some kind of converter, perhaps a table. Then you will perhaps need some low pass filter for the direction. Language? Application of result?
You will need some simple code to gray to binary.
A lookup table, or one Gray code pattern can decode with XOR gates.
See
https://www.elprocus.com/code-converter-binary-to-gray-code-and-gray-code-to-binary-conversion/
I was hoping there might be a prewritten OBJECT for conversion. Otherwise, I may have to attempt a lookup table or something.
Aaron
You shouldn't do that -- not everyone cares about what we care about, and writing a library takes time. Time you seem unwilling to take and then share with everyone else. Am I wrong?
No worries, I'll bite. What's the device you want code for? That detail is important when you're hoping others have written code so you don't have to. I need a rainy Saturday mental challenge so I'll see what I can do. No promises, though.
A few moments later...
Never mind. The neat thing about the Internet is with a bit of searching you can find algorithms for anything. I found one that explained converting Gray Code to binary and implemented it in Spin. I tested with all 4-bit Gray Code values and it works. I also plugged in %10000000 which returns %11111111 as expected. The choice is yours. You can use a look-up table if speed is more of a concern than program space. If speed is not an issue, this routine compiles to 36 bytes according to Propeller Tool.
pub gray2bin(value, msb) : result | n, last '' Convert gray code value to binary '' -- msb is highest bit of value (e.g., 7 for byte) result := last := (value >> msb) & 1 repeat n from msb-1 to 0 if ((value >> n) & 1) last ^= 1 result := (result << 1) | lastJon
I'm not worried about time. If a wheel already exists, why reinvent it! I'd love to share with others (so yes you are wrong) but I'm not as good as 98% of the people on this forum. That being said, I want to get this thing working whatever it takes.
I have a E6CP-AG5 encoder and was planning on using a 74HC165 shift register to send bytes to the propeller where it would be displayed on my big screen as wind direction. The SR and display already works but my home-made magnet and switches on the tower are not so good. I want 16 different outputs to coincide with cardinal directions plus the 4 in-betweens and 1/2 of those. (So North, Northwest and North-Northwest.) Everything in between (the other 239 bytes) is unused. I been reading the one I have about once every 3-5 seconds, so speed is not an issue.
Thanks for your interest. I'll look at that code and see what I can do with it.
Aaron
Not that you asked, but this is what I'd do:
This will give you degrees in 0.1 units, with a resolution of 1.4 degrees.
Paraphrasing and old joke (How do you get to Carnegie Hall?"): code, code, code.
I'm doing something wrong. For input of %10000000 I get 00000001, not 11111111.
Changed var names to mine. What is deg10?
Thanks What's the new way to post code??
Aaron
CON _clkmode = xtal1 + pll16x '80 MHz system clock _xinfreq = 5_000_000 OBJ tv : "tv_text" VAR long winput, gray, EncOut PUB main tv.start(0) EncOut:=%10000000 'also tried % and none repeat ' loop winput := (360_0 * gray2bin(EncOut, 7)) >> 8 go(4,4) 'TV location on screen TV.bin(winput,8) 'also tried hex and dec pub gray2bin(value, msb) : result | n, last '' Convert gray code value to binary '' -- msb is highest bit of value (e.g., 7 for byte) result := last := (value >> msb) & 1 repeat n from msb-1 to 0 if ((value >> n) & 1) last ^= 1 result := (result << 1) | last PRI go(x,y) TV.move(x,y)Yes, you are. Here's proof the gray2bin() method works:
For reasons known only to you, you're converting to tenths of degrees (that's what deg10 means above) and expecting to get 255. Why? The expression you're doing is
360_0 * 255 / 256
...which results in 3585, or %1110_0000_0001 -- the last 8 bits are %00000001. Your code is working as you wrote it -- like this:
Use 3 backticks on the line before and the line after the code. I've edited your code above for you, so you can edit your own post to see how it's done!
With the following code I get %00000001 Should be %11111111, no?
CON _clkmode = xtal1 + pll16x '80 MHz system clock _xinfreq = 5_000_000 OBJ tv : "tv_text" VAR long winput, EncOut PUB main tv.start(0) ' EncOut:=%10000000 repeat winput := (360_0 * gray2bin(EncOut, 7)) >>8 go(4,4) TV.bin(winput,8) pub gray2bin(value, msb) : result | n, last '' Convert gray code value to binary '' -- msb is highest bit of value (e.g., 7 for byte) result := last := (value >> msb) & 1 repeat n from msb-1 to 0 if ((value >> n) & 1) last ^= 1 result := (result << 1) | last PRI go(x,y) TV.move(x,y)No! I explained why in great detail above.
If you're dead set on seeing %11111111 on screen, change your code to:
repeat winput := gray2bin(encOut, 7) go(4,4) tv.bin(winput,8)At that point you can hook up your encoder read circuit and you should see %00000000 -> %11111111 for one rotation. To convert the angular position to tenths of degrees, go back the the expression that you keep tripping over. Put it into a method so your code is more obvious. This will convert the gray code output from the encoder to tenths of degrees, 000_0 to 358_5, which each encoder count being worth 1.4 degrees (14 as tenths).
Jon
In both working it by hand and looking at a conversion chart online, the binary equivalent of G10000000 is B11111111. I think the code you gave me is for B to G
Aaron
You mean like this (that I posted above):
No, it isn't. I did develop a method so I could verify both directions. You can see that below -- but this is the first time you're seeing binary to gray from me.
Here, let me see if I can make it more obvious before I click the IGNORE button. I'll even output the numbers like you do in your post. Good luck with your project; I'm done.
Jon
Thanks for all your time. I'll figure it out eventually. Probably what you said in the 1st place.
Aaron
QUOTE If you're dead set on seeing %11111111 on screen, change your code to:
That's all I wanted!!!
Sorry for the confusion