I am a French electronic teacher using VM110 BOARD with my students as analog input interface.
This year I have bough some new VM110N BOARD for other students. What a surprise to realize that both boards doesn’t return the same value for the same input voltage even if the ATT1 potentiometer is set to the maximum!!!
i.e. A temperature sensor give me 2.94V at 22°C. On five VM110 boards the analog converter give 2.94V which is good but on the other five new VM110N boards the result is 3.09V. These 0.15 volts difference give after adaptation 15 more degrees than the right temperature. This is not acceptable.
I wanted to find where was the difference with the new VM110N board but I have realized that components references was different. So, could you send me the new schematic of this new board. If not, is it possible then to buy the oldest VM110 board ?
Hi,
You can download the schematics for the K8055N (kit)
I think they should be the same except the VM110N uses SMDs
K8055 link
http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k8055_uk_rev3.pdf
K8055N
http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k8055n-uk.pdf
This way you can compare the two
Thank to respond,
Unfortunately, components references of the K8055N are totaly different with the VM110N.
Here is the link to download the VM110N circuit diagram and the PCB lay-out drawing:
box.com/s/rttfjau8szcpulh0fylz
The circuit diagram has been helpful to solve the problem.
The new VM110N board include a PIC18 microcontroler instead of the original PIC16 on the VM110.
Therefore the power supply of 3.3V used for the microcontroler becomes the voltage reference for the analog to digital converter instead of 5V.
To adapt the input voltage, a voltage divider has been placed using standard resistors. Because of the tolerance of the values and the standard value, a wrong division is created.
Here are three ways to solve the problem:
1- Replace R33 to R36 using 1 percent tolerance resistors. Not easy to have some.
2- Solder a 13 kohm resistor in parallel with R33 and R36. Not easy with SMDs.
3- Solder a 20 kohm resistor in parallel with two terminals (not the wiper) of the potentiometer RV1 and RV2. Easy with non SMD resistor solded on the solder side of the circuit board.
Now I get the same and the right voltage using the VM110N board than the VM110 with the software “Profilab-Expert”.