Difference between revisions of "Experimenting with IR Remotes using a PIC running BoostC Project"

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More information on serial communications with microcontrollers: [[Microcontroller Serial Communications Articles]]
 
More information on serial communications with microcontrollers: [[Microcontroller Serial Communications Articles]]
 
  
 
A free terminal program, I like this much better than hyperterminal:
 
A free terminal program, I like this much better than hyperterminal:
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SourceBoost Technologies
 
SourceBoost Technologies
 
http://www.sourceboost.com/
 
http://www.sourceboost.com/
 
 
 
 
  
 
== Download ==
 
== Download ==

Revision as of 18:44, 31 December 2008

Experimenting with IR Remotes using a PIC running BoostC Project

EARLY DRAFT - NOT READY


  • Name: Experimenting with IR Remotes using a PIC running BoostC Project
  • Status: early draft -- do not read
  • Technology: PIC microcontroller, slavaged IR reciever, running with code in BoostC
  • Author: russ_hensel ( where you can find an email address to reach me )
  • Summary: A PIC16F877A project that reads IR remote controls. Runs with a PC running a terminal program.
  • Last revision Dec 21 2008 – Early Draft.
  • Download: see section below.

This project describes just enough software and hardware to let you experiment with infra red remote controls to use as a jumping off point for a more complete project.

Platform: PIC16F877A using BoostC connected via rs232 to a PC running a terminal program. The PIC chip is supplemented with a slavaged IR reciever.


Hardware

Taking apart old VCR's and similar devices you can often find small IR remote receivers. These are outwardly simple devices, an IR sensor looks something like a LED but perhaps hidden behind a grill or filter and 3 wires. The wires are for power ( two wires, +5 volts and ground ) and one for the signal which goes to a PIC input port. Shine the light from an IR remote control ( from a broken, or not TV, the dump or buy a universal remote ) and the output pin jumps up and down for a while. Learn what the jumping means and figure out what button was pressed on the remote. Add a whole new interface to your PIC projects using only one pin.

An IR receiver whose spec sheet is easy to Google is the GP1U58X, this will help you with the pin out. Other information on the receiver and hardware can be found by Googling for the many other projects out on the web.

For the PIC part of the project I use my favorite 16F877A set up as in PIC based Stepper Motor Dancing Analog Clock. Use input RB.0 as it has an interrupt available. Use the UART and a PC for other control of and communications with the PIC as with the Clock.


Schematic

Schematic

Parts -- this is not up to date, working on it

Part Details
Power supply Not shown, 5 volts, you can use a higher voltage with a voltage regulator. There is a suitable power supply in the PIC based Stepper Motor Dancing Analog Clock
PIC16F877A My favorate 16 series part, relatively lots of memory and pins. Bigger than you need, but only about 8 bucks. Try with an 18 series part, should not be hard and will leave you more up to date. Let me know. Other parts of the PIC circuit not discussed here.
Power supply splitting resistors, form a pseodo ground at about 2.5 volts. 100 more or less
RIN about 5 to 10 K
RFB feedback resistor should be about 4 times higher than the input resistor

Command Interface

All commands ( except stop should be terminated with a carriage return ) Note that the command interface is not very smart, giving parameters that are out of range my blow the whole program up. If so reboot the PIC. Do not send a new command ( except stop ) until earlier commands have been completed ( actually you can get ahead some if you are careful )


Command Code Notes, PIC Response
Report version v<cr> Version of the PIC software something like:

Serial Stepper Test ver July 4 2008

Reset r<cr>

reset the counters and the log of the encoder. Response something like "Reset Count"

Log report l<cr> Report the log of data. A series of binary numbers, comma delimited.
Report on all parameters r Delimited by commas something like:
Position of the encoder p<cr> report the position of the encoder, and other counts of encoder activity.
Stop ! Should almost immediately stop long running commands of which there are currently none. Response Stopped.
Other, not understood commands xxx Responds with "!Bad Command = xxx" if the command is not understood.


Notes on terminal program set up.

  • Baud rate should be 19.2K 8N1
  • Most terminal programs can be set to treat a carriage return as a carriage return line feed. Do it.

Some terminal programs will not transmit in lower case ( all our commands are lower case ) unless specially set to do so. Set it to allow lower case.

Microcontroller Program

Design

If you look at the subroutine readIR( void ) you will see the heart of the IR receive. The routine loops each time checking to see if the output of the detector has changed. If it has not it adds one to the period, if it has it records the period and resets the period to 0. When the input goes quiet for a while it is taken as the end of the signal and we exit. Pretty simple.

The software logs the period of each transition at the input pin in units of the time around the receiving loop. The number of log entries is limited to about 100 due to memory limitations. Because the timing is in terms of times around the receive loop the code has been written to make this time ( roughly ) constant despite branches within the loop.

Control of readIR() is normally via an endless loop ( which the stop command breaks you out of ) which:

Listens for quiet on the IR signal, this stops us from starting to receive in the middle of a signal. Setting an interrupt to call readIR() on the next IR signal. Running readIR() Outputting the log or the received signal.

You can take the data from the log and put it in a spreadsheet to try to analyze what is going on. There is much information on IR protocols on the web.

One of my remotes seems to use the NEC protocol and I have added a version of readIR() to decode this signal, it is called readIRNec(). In this protocol there are basically two different low periods of the input, a short one is read as a 0 the long one as a 1. The code seems to work. I got the information on the protocol from [1].


Control of the software is via the serial communications library that I have described in other articles including Serial Communications Library -- BoostC and 16F877A. It yields a command driven interface with the following commands.


Commands

Command Action
! Stop whatever is running, like read ir and and read NEC. Then you can select a new command.
V<cr> Version of the software, responds something like: IR.c version = Dec 29 2008 b
I<cr> Read Ir Data in a loop without decoding. Generally turn log on or you will not see much in the way of results.
N<cr> Read Ir Data in a loop with NEC decoding. Generally turn log off unless you are debugging the decoding.

Response looks something like:

 exit waitForNoIR()
 IR Data = 10001011,01110100,00000011,11111100,
 IR Data hex = 8B,74,03,FC,
 XOR = 11111111,11111111
 
Ln<cr> Turn log report on with n=1, off with n=0. The log report gives the count of periods between all tranitions.
<cr>

Notes on the NEC Decoding

Using the [] as I guide I guessed at the periods infolved in decoding 1 and 0's. The specification say that the odd numbered bytes should be the bitwize not of the next prior byte. I xor these together, if the decoding is right this should yeild a 1111111 which it seems to do. The button <1> decodes to 03 ( the third byte ). Each sucessively higher button goes up by 2. To see more codes, build the project. My transmitter was not actually a NEC but was a Toshiba which is supposed to be the same, perhaps it is. Test stuff yoursel before trusting the code too much.

Compiling

The zip file contains the entire source bootst project. Unzip into a directory and open in source boost. Set the target to 16F877A. See the comments in the program header for other setup before compiling. After compiling my compiler reports something like:

Memory Usage Report

  • RAM available:368 bytes, used:248 bytes (67.4%), free:120 bytes (32.6%),
  • Heap size:120 bytes, Heap max single alloc:95 bytes
  • ROM available:8192 words, used:1239 words (15.2%), free:6953 words (84.8%)

The program seems to be safely under the 2K free compiler limit.

Other Things to Try

Additions/Changes/Modification

  • The 877A is way overkill for this project unless you make it do a bit more. Note that only 1 input pin ( with interrupt capabability ) plus the serial lines are really used.


Possibly useful links

This program uses my: Serial Communications Library -- BoostC and 16F877A

More information on serial communications with microcontrollers: Microcontroller Serial Communications Articles

A free terminal program, I like this much better than hyperterminal: Welcome to our Free Download/New Products Page! http://www.rs485.com/psoftware.html

BoostC – I think the free version is enough to compile the program: SourceBoost Technologies http://www.sourceboost.com/

Download

pending, not at: Version 1 zip file: StepperTest_v1.zip

Comment, Questions, Contributions?

Email me russ_hensel, or use the talk page for this topic. All feedback is welcome.