A few months ago a friend of mine -car mechanical at profession- told me that he had problem with some car sensors. He couldn't check, with a simple multimeter, if a sensor was working properly. I advised him to buy a LCD oscilloscope instead of a normal oscilloscope, because of its small size. The use of an oscilloscope is very helpful because you can see the waveform that is produced by a "healthy" in-circuit-sensor* and you can compare it with the waveform of a "suspect" in-circuit-sensor.
After that, he told me that this oscilloscope costs a "fortune" for him as he has a small car service shop. I offered to help him by designing and constructing a small, cheap and workable LCD oscilloscope for him.
*in-circuit-sensor is the sensor which is connected on a board (PCB) or it's connected somewhere in the car. It's not a disconnected sensor.
You can download the source code, hex, schematic diagram,PCB and picture of the circuit .
Step 1: Selecting the Components
Step 2: Designing the Schematic Diagram
After I had chosen the components, I had to draw the schematic diagram of this circuit. For this purpose I used the Splan 5 that is not freeware but it is a very cheap schematic diagram software.
Step 3: Making the Prototype
Step 4: Putting the Components in Order
I made my PCBs by myself by using toxic chemicals. That's why I don't describe the procedure. It's very dangerous. I suggest you to give the transparency that you will print to a professional to make the PCB for you.
Step 5: Soldering, Calibrations and Usage.
Solder all components on PCB, starting from the smallest and go on to the biggest component. Check the PCB from soldering side for shortcuts that could have been made during the component soldering. Remember to put IC3 on a base, so the removal for future reprogramming can be done very easily.
If everything is ok, supply the circuit with 12V Dc. On the screen you will see the oscilloscope's raster with a horizontal line on it. Adjust P1 (LCD contrast) with a small screw driver up to the point you will see clearly the content of the screen. If you adjust the P2 you will see that the horizontal line (beam) will be moved up or down depending on the adjustment of P2. Adjust the P2 to set the beam at the center of the screen.
Connect a 1:10 probe at BNC connector (K1) of oscilloscope. Now you are ready to make your own signal measurements. Take care not to exceed the maximum input voltage which can be up to 24V Ac or 30V Dc on 1:10 selection prob. At 1:1 the maximum input voltage can be up to 2.5V Ac or 5V Dc. S1 gives an extra input voltage division by 2. With S2 you can select between AC or DC input signals.