~ Sanjay Tumati
We have an electronics lab as part of STEM land and students who are interested including the old students who have studied in STEM land either at Isai ambalam school or Udavi come to the lab to learn and build things using electronics. This blog is to share one of their experiments at the lab.
The students were excited as they were going to do an interesting experiment in the lab. One wave of the hand over a sensor would turn on an LED and another wave would turn it off. However, the entire experiment was ruined by faulty D Flip Flops (from now on referred to as DFFs). It was not a complete loss. The students learnt how to test a DFF (Reliability via connectivity and functionality via understanding a DFF
- Connect the power supply and ground and observe the current display on the power supply. Some devices heated up immediately drawing hundreds of mA from the supply
- Some devices started heating up on connecting Set and reset pins to ground
- Some started heating up on connecting other connections
- Students did connectivity checks between Set/reset/Clock/Data pins to supply and ground and found that in the faulty ones, the resistances were in the order of 100s of Ohms and not open circuit as was expected.
- Just a couple of DFFs out of a dozen worked and those also went bad in a few minutes
This is the site from where we ordered the DFFs, Buy Electronics Components Online in India – Electronic Components Store
Surprising, because this site is usually very reliable and they send us quality components. We also ordered the CD4013 which is from the venerable CD40xx series. What did we do wrong with the DFFs? It can’t be that DFFs are uniquely susceptible to ESD handling. CD4017 and CD4033 which use several of these were just fine.