[An old project I moved from my previous website]
This is a test project built hastily on a solder less breadboard. It uses a LM75 to read the current temperature via I2C and displays the result on three 7 segment displays. It uses a PIC16F628 with an internal 4 Mhz clock.
The program was created using JAL
Note the LM75 is a surface mount device, so I had to solder wires onto it to use it on the solderless breadboard.
LM75 Temperature Sensor on breadboard
Sorry for the bad quality photo. The stuff on the left is a 5V voltage regulator and not shown on the schematic below.
LM75 Temperature Sensor Schematic
Component List
Part Value Device Package Library Sheet D1 7SEG-CA 7SEG-13 special 1 D2 7SEG-CA 7SEG-13 special 1 D3 7SEG-CA 7SEG-13 special 1 IC1 PIC16F628 PIC16F628 DIL18 microchip 1 IC2 LM75 LM75 SOP-8 andre_lm75 1 Q1 BC557C BC557C TO92-EBC transistor-pnp 1 Q2 BC557C BC557C TO92-EBC transistor-pnp 1 Q3 BC557C BC557C TO92-EBC transistor-pnp 1 R1 12K R-EU_0207/7 0207/7 rcl 1 R2 12K R-EU_0207/7 0207/7 rcl 1 R3 1K R-EU_0207/7 0207/7 rcl 1 R4 1K R-EU_0207/7 0207/7 rcl 1 R5 1K R-EU_0207/7 0207/7 rcl 1 R7 220 R-EU_0207/7 0207/7 rcl 1 R8 220 R-EU_0207/7 0207/7 rcl 1 R9 220 R-EU_0207/7 0207/7 rcl 1 R10 220 R-EU_0207/7 0207/7 rcl 1 R11 220 R-EU_0207/7 0207/7 rcl 1 R12 220 R-EU_0207/7 0207/7 rcl 1 R13 220 R-EU_0207/7 0207/7 rcl 1 R14 220 R-EU_0207/7 0207/7 rcl 1
In case you are like me and couldn’t find the pinouts for the sevent segment display, here they are:
7 Segment Display Pinout
Download the project here: LM75 Temperature Sensor Project - LM75 Temperature Sensor with 7 segment display output. Uses a PIC Controller. This project includes the JAL source code, a compiled hex file and a schematic.
#1 by Brian Anderson - March 27th, 2009 at 00:05
I am trying to recreate your project as you have graciously laid out for a novice such as myself. The difference that I have made, is that I am trying to increase the scale of the LEDs to 4″ requiring 3.3v max on each segment. Any ideas on the pitfalls that I may encounter? BTW, Great looking website!
#2 by andre - March 27th, 2009 at 11:21
I have to admit, its been a long time since I tinkered with this stuff, but I expect that with the correct value resistors you can limit the voltage to 3.3v.
#3 by Chris - April 1st, 2009 at 11:22
Hi, i have reproduced your project. And i was so amazed it worked great. The only problem is the LM75 chip that seems to come only on SOP package. Isn’t there any adapter or converter to DIP or something?. Anyways, you are awesome.
#4 by Brian - April 1st, 2009 at 20:50
Newby here again. To program the PIC I am using a PICkit2 and a small bred board. Is there a guide how to wire the bred board as an interface between the PICkit 2 and the 16F628?
#5 by Brian - April 2nd, 2009 at 03:01
I found the PICkit 2 programmer adapter design from http://www.sq-1.com/pickit2.html It appears I was successful at programming my chip with your HEX file. Awesome!
#6 by Brian Anderson - April 2nd, 2009 at 21:28
Now I am about to power up my thermometer. I am trying to determine how many amps should the 5V regulator have. Is there any additional wiring that I should do? Ideas?
#7 by Chris - April 6th, 2009 at 10:39
This project is quite simple as the author has wrote in the previous site on 100acre.org . I had no problem at all in order to make it work, once again great job for beginners on electronics like myself. To me the hardest part was to solder wires to the LM75, but i am already contacting a taiwan supply company that makes SOP to DIP adaptors (www.cpu.com.tw) to bypass that problem. Except that, i believe everything else works fine to me. By the way, does your voltage regulator is a LM7805?, i use one, but checking on national.com, its already discontinued. Good luck Brian.
#8 by ashok - April 23rd, 2009 at 15:54
where to get LM75 and PIC16F628 from?
#9 by Chris - May 14th, 2009 at 06:59
The answer. Digikey (http://www.digikey.com) they provide an excellent service, another choice can be Allied electronics (http://www.alliedelec.com), their service is also good.