48 lines
3.0 KiB
Plaintext
48 lines
3.0 KiB
Plaintext
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This is a simple FM wireless microphone. It will transmit about a mile.
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___ ______________________________________________________________
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\|/ ___ ) | | | | | |
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| --- ) R ___ R R | -----
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|_||__| C10 ) L1 4 --- C3 5 7 | ---
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|| | ) | | | | ___ C6 ----- B1
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C1 ------- | | | | --- --- 9VDC
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|_____ | | C9 __R6__ ---- | |
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| \ Q1 | | | | | | | |
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| \|______|_______|__|(__| Q2 | R | | |
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___ /| | | |( \ | C5 8 | | |
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C2 --- / BF199 | | \|___|__|(___| _+_ | |
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|____V R | /| |( | --- | o
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| 2 ___ / BC183C | | C7 | \
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| | C4 --- V | | | \ S1
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R | | |_______ MIC / \ | | \
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1 | | | | \_/ | | O
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| | | R _+_ | | | |
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| | | 3 --- C8 | | | |
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| | | | | | | | |
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---------------------------------------------------------------
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R1 = 100 ohms C1 = 1.5 pf NPO ONLY Q1 = BF199, ECG 229,
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R2, R4 = 10K ohms C2 = 100 pF, NPO ONLY 2N5179 or eq.
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R3 = 1K ohms C3, C4 = 330 pF NPO Q2 = BC183C, ECG123AP
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R5, R7 = 47K ohms C5, C9 = .1 uF 2N4401 or eq.
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R8 = 4.7K ohms C6 = .001 uF NPO ONLY L1 = approx. 1 uH
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M1 = electret mike C7 = 22 uF electrolytic S1 = SPST switch
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B1 = 9V battery C8 = 6.8 uF electrolytic
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C10 = 10 - 40 pF trimmer capacitor.
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The coil L1 is so small that in the PC board version of this, it's just a coil
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etched on the board with traces. I think I breadboarded it with about four or
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five turns of bell wire around a pencil and that made about the right value.
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You tune the sucker with the adjustable cap C10. If I remember, the
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transistors are garden variety ones, though I think Q1 was reasonably high
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frequency. I was feeding in a signal other than an electret microphone.
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This is neat to use with a cheapo FM walkman-type radio for cheap telemetry.
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(We were actually going to build a device to transmit strain gauge signals
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from someone's teeth over a whole day's time, and it was to be small enough
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to be relatively unnoticed INSIDE THEIR MOUTH the whole time. Never did
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get the O.K. to proceed with that one. Working for university research
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gets pretty strange sometimes.)
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