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A watchdog
for SSTV transmitter. (Par example for the Telefunken Teletron T813.) This circuit occurs the PTT to activate continue constantly. Because SSTV causes long time transmitting a digital counter CD4060 is being applied. In rest without PTT active the circuit is hold in reset. As soon as the PTT is active, the reset is raised the oscillator is going to work and the counter is counting. The led is flashing on the oscillator freqency (app. 2.5Hz). So you can see the PTT is active and the transmitter is working. The watchdog will be active after 3.5 minutes as Q10 rise high. The oscillator stops and locks the BS250. The transmitter stops also and the led lights continu. This situation is raised after the PTT get inactive again and the circuit resets. |
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The watchdog
time is to be variated by another choice to the outputs of the
CD4060 and/or another resistance R4 (100k.. 1.5M). Instead of a BS250 you can choose a (pnp)darlington with using a basisresistance 100k. At least use also a 10nF along tje powersources of the CD4060. Of course, but it is not to be seen in the schematic.
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73 Jeroen, PE1MWB |
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Uhh ja, heeft u alles eigenlijk wel gezien? Of wilt u toch nog even terug naar het begin? | Of toch nog even kijken naar de andere projecten? | Link to: |
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© Overname van artikelen alleen NA toestemming (meestal heb ik geen bezwaar voor HAM-radio doeleinden) |