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Using TMP100 temperature sensor with your PIC – PR5

January 31st, 2012 No comments

In this post I will describe how you can connect the TMP100 temperature sensor from TI to your PIC as well as receive temperature data. The sensor I am using is a generous sample from TI. Compared to the DS18S20 that I used before, this sensor is much faster, it takes 40ms to take a measurement with 0.5 degrees accuracy. The communication protocol is I2C. It could be a bit difficult connect it to your circuit since it is using a SOT-23-6 package.

For this project, I will be using my PIC prototyping board which carries a 18F4520. But you can pretty much use the C18 code in this post, with any PIC having a hardware I2C module.

Package problems!

Because SOT-23-6 is so small the first thing I needed was to create an adapter to make TMP100 compatible with my breadboard. This was a perfect excuse for improving my CNC skills :). So I created an adapter in EAGLE, cut it out using the CNC and then solder the sensor and 6 pins. The sensor is now breadboard ready!

The TMP100 adapter

 Connection

The connection is really simple. Add two pull-up resistors to the SDA and SDL lines. I used 10kOhm. The datasheet also suggests an optional capacitor on the supply.

TMP100 pinout

 

TMP100 Schematic

As you can see from the schematic there are two pins called ADD1 and ADD0. Those pins determine the I2C address of the sensor. You can find more details in the datasheet. I connected those two lines to GND therefore the address of the sensor I am using is 0x90. That’s all on the hardware side.

TMP100 – Point Register

I2c is the language this sensor talks :). So we need to use your PICs I2C hardware capabilities. Initialize your communications using

OpenI2C(MASTER,SLEW_OFF);

This sensor has a Point Register (PR)which (guess what!) points to the address of the register you want  to read or write :) Before doing anything else we should point PR to the temperature register. To do that we have to initiate an I2C communication, send the address of the sensor and tell that sensor whether we like to write or read from it. This is done using a single byte. You see, the address is 7-bits starting from the MSB and bit 0 indicates whether is read or write operation (0=Write 1=Read). Let’s do an example. Our sensor’s address is 0x90. We wish to read something from the sensor so the byte should be 0x91. If we wish to write something to the sensors it should be 0x90. That’s it.

Therefore to write to point PR to the temperature register we should issue the following

StartI2C();
WriteI2C(0x90); // Call the sensor with WRITE
WriteI2C(0x00); // Write Temp reg to point register;
StopI2C();

Notice the 0x00? That is the address of the temperature register. The sensor is now ready to give us some temperatures.

TMP100 – Read that temperature

To read the temperature off the sensor, we need to call it using its address and READ (what we said above, remember?) and the sensor will transmit two bytes of data back. We read that using the appropriate I2C commands shown below. We have to acknowledge the reception of the bytes to let TMP100 know that we are ready for the next byte. Temperature is read as follows

StartI2C();
WriteI2C(0x91);
first_byte = ReadI2C();
AckI2C();
second_byte = ReadI2C();
StopI2C();

The temperature is made out of two bytes. If you don’t care about getting any decimals you can just use the first byte. The 4 most significant bits of the second byte contain information on the decimal value of the temperature.

TMP100 – C18 Library

I made a really simple library for tmp100 in C18. Just include the tmp100.h file to your project and make sure you initiate the I2C (the OpenI2C() command shown in this post) before calling any functions.

 

OK that is pretty much. You should be able to get some measurements out of that little sensor. If you need further help take a look at the example below

#pragma config OSC = HSPLL
#pragma config WDT = OFF
#pragma config PWRT = ON
#pragma config LVP = OFF
#pragma config PBADEN = OFF
 
#include <p18cxxx.h>
#include <i2c.h>
#include <usart.h>
#include <delays.h>
#include <p18f4520.h>
#include <stdio.h>
#include "tmp100.h"
 
void main(void) {
 
    unsigned int raw_tmpr;
    char str_tmpr[8];
 
    OpenUSART(USART_TX_INT_OFF &
              USART_RX_INT_OFF &
              USART_ASYNCH_MODE &
              USART_EIGHT_BIT &
              USART_CONT_RX &
              USART_BRGH_HIGH,
              21);
 
    Delay10KTCYx(250);
 
    OpenI2C(MASTER,SLEW_OFF);   // Initialize I2C module
    tm_setconf(0x60);   // Set sensor to full sensitivity
 
    while(1)
    {
        Delay10KTCYx(500);
        raw_tmpr = tm_gettemp();    // Get 2 bytes of temperature
        tm_tostr(raw_tmpr,str_tmpr);    // Convert the temperature to text
        printf("Temperature is %s\r",str_tmpr); // And output through USART
    }
    return;
}

I connected the USART TX/RX line using my CP2102 and used the cutecom program on Ubuntu to read the output on my PC. The screenshot below shows the terminal

The terminal on Ubuntu

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Serial Interface Between PIC and PC – PR4

October 4th, 2011 2 comments

This one is really useful.

Most of the times you are developing a project, you will need some sort of monitoring or visual output to understand the status of your program. Sure some LEDs blinking are great but some times you need more. This is where the good old serial communication comes in. Through this communication you will be able to send information in the form of data or text, to and from your computer. You can use it as a debugging tool to monitor what is going on in your microcontroller during execution time. Or you can use this communication to send data to the PIC for processing and then receive the result back. I am sure you will appreciate the usefulness of this as soon as you implement it.

And all this happens by sending a sequence of zeros and ones… Read more…

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PIC and 5110 Interface with SPI hardware – PR3

September 26th, 2011 11 comments

This is the first “official” project I am doing with my PIC prototyping board. This project is about interfacing and using a simple Graphic LCD. So to follow this project you need a PIC to have SPI hardware, in order to communicate with the device. The GLCD (Nokia 5110) I am using is well known in the community and it is a cheap device. I bought it off ebay for about 5 Euros. Read more…

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PIC Prototyping Platform – PR2

September 7th, 2011 No comments

Hey,

In PR1 project, I talked about creating a stable prototyping platform that would save me from the trouble of setting up the microcontroller and all its required components. However, since then, I worked on tidying up this design into a more usable design (I wanted to play around with creating PCB actually :D ). So I designed the board sent it for fabrication and finally put it together. Read more…

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Total Beginner’s PIC Platform – PR1

April 27th, 2011 No comments

So I was thinking its time to start posting some complete projects. I am starting with some really basic projects to help the people just starting with PICs. However, before doing that we need to have a common platform to develop on, so we don’t need to discuss about it every time. In this first project (see how I codenamed it PR1!) we will create a minimal PIC platform which we will use in future projects. I will list everything you will need to buy to get you started.

As the brains of this platform I am choosing the PIC18F4520 which I believe it is a pretty nice PIC to work with, having enough peripherals, memory and speed for any beginner project. Let’s see the components you will need:

  1. Breadboard – if you don’t have one, you really need to buy one!
  2. PIC18F4520
  3. 10MHz oscillator
  4. 2 x 22pF capacitors
  5. 10kOhm resistor
  6. 7805 Voltage regulator
  7. PICKit 2 (or 3)

Using the above components will allow to build a functional board even though more components are needed to be “perfect” (smoothing capacitors on the regulator, a couple of diodes between the programmer and the supply and more). Of course it would be nice to add a switch, a reset button, LEDs, and the list goes on, but this would increase the cost of the board. Consider this as a quick-and-dirty solution just to get you started. Maybe on a future post we create a more complete board. For now I believe this is a good starting PIC testing board.

Using the schematic below, hook up the board. I am also attaching a photograph of my own testing board for reference. You also need some sort of power. I find it convinient to use the 9V battery holder and connect it either with a 9V battery or a power supply. Feel free to use any kind of power supply as long as it is between 6V and 12V. If you are (somehow) using a 5V supply, take the 7805 regulator out.

After connecting everything it would be a good idea to write a simple program to check the functionality of the board. I have a simple LED blinking program already compiled. So, using your programmer, transfer the HEX file (attached at the end of this post) to your PIC. To test this out you will need an LED and an 1kOhm resistor connected to the A0 pin as shown in the figure. Turn on the PIC and the LED should be blinking every 1 sec. If not then something is wrong :). But don’t worry. The board is simple enough to figure out where the mistake is and if you have trouble you can always ask me.

So now you have a board to play with :)

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