In the the last few months I have found myself studying electronic circuitry to get to the bottom of some complex vehicle faults . Now a few years ago I would never imagined I would have an understanding of transistors,resistors,diodes,capacitors and how they contribute to a working circuit.
Now I am no expert on the subject and I have so much that I still would love to learn about , But taking my knowledge of electronics to the next level has been hugely beneficial to my understanding of vehicle diagnostics, the way I carry out tests with the oscilloscope and multi meter and also why components or circuits fail in the way they do.
I have written this month’s blog in the hope that someone who enjoys diagnostic work as much as I do might be inspired to further their own knowledge of vehicle electronics .
One of the circuits that inspired me to dig a bit deeper into this subject was explained to me by John Batten of AutoIQ in Northampton , and it is the H-Bridge circuit .
The H-Bridge circuit has so many applications in vehicle electronics , Before I had this explained to me I didn’t even realise how many components can be controlled by using this design. The throttle body motor is probably the most obvious use , but other applications can include EPB motors, Power windows, HVAC motors, Seat adjusters and many more. I am not going to go into too much detail as like I said I am no expert and there are many sites that will explain it in great detail far better than I ever could , But take a look at the circuit below and the waveform of a throttle body sweep from closed to wide open and back again. You can see how the path of current is controlled by the transistors switching and there are diodes ( or one way valves) to stop back emf from delivering any voltage created by the motor moving in reverse(generating voltage) back to the computer. Knowing how that motor is now controlled inside the ECU helps understand the waveform and makes a definitive diagnosis of this component much easier.
Another circuit design I have been studying is the Wheatstone bridge (or Null comparator) , this is used in Thermistor and Transducer circuits . It uses Ohms law to measure resistance very accurately which gives more precise feedback to the processor of temperature or pressure.
I have also spent a lot of time looking at Pull up and Pull down circuits which is knowledge I now use on a daily basis when doing circuit tests . Again if anyone reading this does not know what they are or how to determine which is which please take some time to find out , I promise you the next time you are diagnosing a possible sensor issue on the vehicle and you understand how these circuits work it will make it much easier to set up simple tests and manipulate the circuit to confirm a 100% accurate diagnosis.
If you know all about these circuits and understand them fully then please share that knowledge with those who might benefit, After I was inspired to dig a bit deeper my knowledge has expanded greatly and I really hope my blog inspires even just one other person to become even more passionate about the subject and use it as a stepping stone to the next level.
Glenn Norris CAE AMIMI