Temperature Sensor (LM35) and Bar/Dot display (LM3914N)

[Rhondeed]

I need help, can anyone give me some directions PLEASE. I have to design a temperature sensors using a LM35DT and a bar/dot display LM3914. I have no idea on how to interface these to chips together to ensure that it will work problem. Any help and direction will be greatly appreciated. If you have any websites that I can obtain this information from, I will greatly appreaciate all direction on this project. My deadline date is Sept. 21, 2004.

:lol:

 

[k7elp60]

Since the LM35 is a temperature sensor with an output of 10mV/degree C
and the LM3914 is a bargraph that can be configured to indicate a change in voltage, and thus would indicate temperature.
What specifically do you need help with?

 

[Rhondeed]

Temperature Sensor (LM35) with Bar/Dot display (LM3914)

Thanks for your reply. I need help with hooking the two chips together. I don't know what size capacitors or resistors I should use. I have a slight idea but it didn't work. The testers will put a blow dryer on the sensor to see which Led's light up. Each pin on the LM3914 that is connected to an LED should carry a certain degrees. I don't know if that makes sense to you but any direction and help you can offer will be greatly appreciated.
Thanks again

 

[k7elp60]

The easiest would be to use the LM3914 in its basic mode. Thats to use it as a 0 to 1.25 volt indicator. The LM35D has a maximum temperature of 100 degrees C. The output at 100 degrees C would be very close to 1V.
Connect the out terminal of the LM35D directly to pin 5(sig in) of the LM3914. Connect the other pins of the LM3914 as follows. 10uf electrolytic capacitor + to pin 3. - of capacitor to pin 4. Connect approximately 12V + to pin 3. - to pin 4. Connect pin 8 (ref adj) to pin 4.
Connect pins 6 and 7 together. Connect 1.5K ohm resistor from pins 6 &7
to pin 4. Connect Vs pin of LM35D to pin 3 of the LM3914. Connect gnd pin of LM35D to pin 4 of the LM3914.
The 1.5K ohm resistor sets the LED current to approximately 8.3 Ma. The first LED will illuminate at 12.5 degrees C and each succeding one will illuminate at the next 12.5 degree step. The last two may or may not come on.
Hope this helps