Greetings forum members!
I am a new member, and first time poster. I am working on a thermometer circuit for a university project. I have constructed a thermometer circuit used to read in Celsius to complement a solar cooker project we are undertaking in my engineering class. I built the circuit on strip board, using a published circuit diagram. The thermometer as assembled powers up and reads digits on the LCD display, and I can use the zero adjust pot to change the temperature.
My problem is this; the thermometer can be adjusted to read zero with the probe in ice-water, but then when placed in boiling water it reads over 500 to 600 units. No adjusting with either the zeroing pot nor the gain adjust pot can make it read zero in ice water and 100 in boiling water. It still responds by increasing digits in hot water and decreasing digits in cold water, it just seems to be logarithmically off somehow.
I have attached the schematic that I used. I made a substitution where C2 is now a .33uF cap instead of a .27uF cap. I also included a 5V regulator with a LM7805 to bring the 9V battery down to the correct voltage. Everything else is exactly the same as the diagram.
I'm not sure what could have gone wrong. I am a relatively new at this, and I don't fully understand how the components interact. I have seen the CA3162 and CA3161 used as a digital multimeter, and some of those diagrams use voltage dividers before they input to the CA3162. Could it be that a voltage divider is necessary, or could it be that this thermometer as constructed can still be adjusted to read in Celcius?
Any and all help would be appreciated. All questions will be answered promptly. I can also provide more pictures and diagrams, as well as a parts list, if requested.
Thank you in advance,
Joshua in England
View attachment 60521
View attachment 60520
I am a new member, and first time poster. I am working on a thermometer circuit for a university project. I have constructed a thermometer circuit used to read in Celsius to complement a solar cooker project we are undertaking in my engineering class. I built the circuit on strip board, using a published circuit diagram. The thermometer as assembled powers up and reads digits on the LCD display, and I can use the zero adjust pot to change the temperature.
My problem is this; the thermometer can be adjusted to read zero with the probe in ice-water, but then when placed in boiling water it reads over 500 to 600 units. No adjusting with either the zeroing pot nor the gain adjust pot can make it read zero in ice water and 100 in boiling water. It still responds by increasing digits in hot water and decreasing digits in cold water, it just seems to be logarithmically off somehow.
I have attached the schematic that I used. I made a substitution where C2 is now a .33uF cap instead of a .27uF cap. I also included a 5V regulator with a LM7805 to bring the 9V battery down to the correct voltage. Everything else is exactly the same as the diagram.
I'm not sure what could have gone wrong. I am a relatively new at this, and I don't fully understand how the components interact. I have seen the CA3162 and CA3161 used as a digital multimeter, and some of those diagrams use voltage dividers before they input to the CA3162. Could it be that a voltage divider is necessary, or could it be that this thermometer as constructed can still be adjusted to read in Celcius?
Any and all help would be appreciated. All questions will be answered promptly. I can also provide more pictures and diagrams, as well as a parts list, if requested.
Thank you in advance,
Joshua in England
View attachment 60521
View attachment 60520