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ghostin

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Posts: 3
Reply with quote  #1 
I'm a college student doing a project involving your kit 49 and would like to have some help trouble shooting it. Ive spent 2 weeks trying to get this to work with help from my professors
Thanks
Frank

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Posts: 1,890
Reply with quote  #2 
Am here to help. What is the problem?

Some questions before we start:
1. Did you assemble the kit yourself or buy it already assembled?
2. What power source are you using to power the kit?

ghostin

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Posts: 3
Reply with quote  #3 
I put it together. I'm IPC certified for class 3 soldering as well. i'm using a 9V battery. The problem is in the transmitter circuit. It osculates at 250kHz.   i originally had this problem and then because of a time crunch i bought another kit which the transmitter circuit worked sending out a 40khz 17Vp-p square wave to the transmitter, but on the receiver side it after the first op amp the signal would never go low so no signal ever went through the diode. 
The first circuits receiver circuit was believed to work because I put a 40khz signal a crossed the transmitter with a function generator and the circuit worked. Once again this is a project for my final college class, so im under a big time crunch. I replaced the crystal in the 1st project with the 2nd project's, where the transmitter circuit was working.

after all this the transmitter circuit on the first project with the new crystal once again is outputting a ~250khz  signal but it has mV's of p-p

thanks
Frank

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Posts: 1,890
Reply with quote  #4 
Firstly, the Tx and Rx transducers are different. The Tx has a 'T' suffix on the number stamped underneath it. The Rx unit has an 'R' suffix. Please check you have them connected correctly on the PCB.

Having said that, I seem to recall that they may have switched to a different transducer type where both the Tx and Rx were the same ie. doesn't matter which connects where. Still pays to check anyway.

The 40khz oscillator is relatively straightforward so I'm guessing the problem will be either incorrect component placement or a soldering problem, either poor solder joint or solder splash causing a short.

Another common problem is that IC pins can get bent under the IC body when inserted into sockets. Suggest you remove IC2 (4049) and check the pins.

There is always the possibility that one of the PCB traces may have fractured, especially with single sided PCBs.

I assume you have access to a oscilloscope. I suggest powering up both kits and doing a side by side test. On the good transmitter board check the output on pin 6 of IC2. Follow it through to pins 3 & 5 and also pins 2, 4, 9, 11 & 14. Then do the same on the non-working board. The oscillator circuit is so simple it should be relatively easy to find the fault.
ghostin

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Posts: 3
Reply with quote  #5 
As i stated before I'm IPC certified (class 3 solder work)  i've checked all the solder joints none of them are the issue. The Tx and RX transducers are in the correct placement. All components are in the correct places. the board doesnt have any cracks or lifted lands. i do have access to an oscilloscope and i've looked through the circuit. i've also had a new board sent to me and the new boards transmitter circuit is working but the receiver circuit isn't. the voltage never can get more negative then the other side of the first diode allowing no voltage through.
Frank

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Posts: 1,890
Reply with quote  #6 
Since you have an CRO then I suggest you do a side by side test.

Very easy on the transmitter circuit.

Bit more difficult on the receiver circuit but simply a matter of following the incoming signal from input through the circuit.

With more info I may be able to help you with some suggestions. Hard to offer any troubleshooting tips 'sight unseen'.
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