AllPro Adapter Kit
I love thru-hole components. It reminds me of years tinkering back to the college times. Yet surface-mount technology almost completely replaced thru-hole everywhere. Manufacturers are not using them for PCB design anymore and newer parts are only offered in SMD form. Some legacy ICs are still there for historical reasons, like LM741 op-amp or 74HCT04N logic IC. Are the days of thru-hole PCBs gone? It was a challenge to build AllPro Adapter in a kit form using only thru-hole components. The LPC1517 chip is only available in a standard small outline surface-mount form factor, so it should stay this way. The rest of components are still available in thru-hole package. Here is the schematic. Fortunately, Microchip is still offering many their ICs in a DIP package, making them available for hobbyists.
The OBD-II Cable for kit
The adapter uses nine pin D type female connector to link up to vehicle's OBD-II J1962 connector. The pinout is De-facto a standard for OBD cables. The cable available on eBay or AliExpress from many vendors.
||J1850 Bus +
||J1850 Bus -
||Vehicle Battery Positive
AllPro adapter PCB components layout
The component placing is shown below:
The printed circuit board layout in Eagle 7 format:
Using simple transistor driver for K Line
Here is another circuit with minimum ICs. The MCU controls the ISO K Line output through MOSFET transistor Q2. Pin 8 of the LPC1517 reads this data through the R16/R15 voltage divider. The pin 8 is configured with hysteresis on and these resistors provides a large amount of noise immunity while also protecting the IC.