Project: Discontinuous Interference Analyzer System Test Circuit

Discussion in 'The Completed Projects Collection' started by Bill B, Aug 29, 2016.

  1. Bill B

    Thread Starter Active Member

    Nov 29, 2009
    After a lot of on again off again work on this circuit I finally have it working. A while back, at work, I discovered the discontinuous interference (click) analyzer hadn't registered anything for several consecutive tests. I used a signal generator and 555 timer circuit to troubleshoot the system and discovered we had a broken input cable inside the analyzer. A quick solder job and it was back up and running. The boss decided that we needed a permanent system to verify our setup before testing.

    The click test measures short noise events on the power mains that are generated by a tool or appliance connected to the circuit. These noise events are characterized as short clicks (<10ms) or long clicks (>10ms). There are four channels monitored by the system, 150kHz, 500kHz, 1.4MHz, and 30MHz. I needed to generate these 4 frequencies and switch them on and off sequentially for a specified duration with a consistent period of time between switching events.

    For the 3 lower frequencies I used 74HC14 Schmitt trigger inverters with an RC feedback network to set the frequency. For the 30MHz signal I used a canned crystal oscillator. Each oscillator output was connected to an input of a 74HC00 NAND gate. I used a PIC12F629 micro to enable the NAND gates for 8ms, 17ms, and 25ms (click durations) with a 10 second interval in between each click duration. I used a series base resistor and potentiometer on each output to control the amplitude and series caps on each output for decoupling. The outputs are all connected to a 2n4001 transistor configured as an emitter follower buffer and then fed to a pair of X-caps that couple the noise onto L1 and neutral of the power mains. I generated the micro programming code using Flowcode. The best part of this project (especially where management is concerned) is that I was able to use parts that were laying around the lab to build it with the exception of the PIC micro, which is cheap anyway.

    Attached is a picture of the board, final project, source code, and schematic. Thanks to all who provided advice and support on this project.