cjack posted:Thanks. 5 v supply?
Essentially yes, the 3.3 ohm resistor is in series with the input to the 78L05 5V IC regulator chip. What thru me for a loop is this version of the R2LC (maybe all do this) has a diode in the ground-leg of the 78L05. This raises its output voltage by one diode drop or to about 5.7V (instead of 5V). Elliot said he couldn't read any voltage on the 3372 chip so I knew there was a problem in the 5V circuit...but I had to scratch my head for a bit when I couldn't find a connection between the 3372 ground pin and the 78L05 ground pin!
Big_Boy_4005 posted:Well done Stan! You made that look easy. The audible signal idea is interesting, as long as the pitch range is easy enough to differentiate between adequate and substandard levels.
That's an interesting point. As Dale points out, this is a "relative" tool where there's no absolute threshold. The meter circuit on these chips has quite a bit of variation chip-to-chip so 2 different R2LC boards can give materially different readings for the same signal strength. I was thinking more in terms of hearing the tone go up and down in real-time as if someone is telling you you're getting warmer or colder. That is, you really need to look at the recovered TMCC digital signal at the output of the 3372 to know if the signal is good. Obviously you could have a monstrous interfering 455 kHz signal from wherever that would measure as a high level but be useless. You are now entering the Twilight Zone of so-called Bit-Error-Rate instrumentation which has its role in the universe but probably not in the world of TMCC. If I do come up with something you'll be getting it when I return your R2LC so you can be judge and jury!
cjack posted:Or this...
Yes, that's what I was thinking since the 555 has oomph to drive a speaker. The design problem is whether the 3372's meter output pin with its microamp current-output can drive the 555 without a bunch of additional circuitry. Additionally, the DC power to drive the 555 and speaker has to come from somewhere. Burdening the on-board R2LC's 78L05 may be asking too much to drive a speaker so Dale's 9V battery might be the way to go. Classic case of all ideas eventually degenerate into work!
