also the pickup circuit could be eiether a opamp or a comparator... i guess the comparator would stabilize the signal to something useable for pin 14 of the PLL chip
any thoughts?
The OpAmp is just used as a Schmitt-Trigger. If the voltage from the pickup-coil is positive, it will output a high signal. If it's negative, it will output a low signal for the PLL. With the 1M/100K feedback you adjust the hysteresis.
Edit:
It's interesting. As I looked again at the original VIC-PCB, I discovered, that not even the LED is connected to the dividers. The LED is directly connected to the signal (the orange/white wire on the bottom left). This actually means, that the 3 divider chips were not used at all.
It's also funny to note, that it seems the Inhibit signal, that's coming in from the external control, seems to have a different voltage level. Therefore he needed to add a level translator (Pullup with a germanium diode, in the lower left).
Edit2:
Seems like the server is having some real problems, the last few days, or is it just me?
I thought again about the strange feedback wiring into the comparator of the PLL, that Stan made (the second blue wire). IMHO there's only one good explanation for this workaround, and why he didn't connect the output of the VCO to the comparator input (like it is usally done, and like in the patent pic). He uses quite a transistor cascade. If the driving delay is too big, then the comparator would already see quite some phase differences between this signal and the pickup-signal. Like that e.g. the Lock-in detector could then detect a not locked-position, although the resonance frequency is hit. If you connect directly the driving voltage of the primary to the comparator, then you certainly get rid of this transistor driving signal delay.
But on the other hand, one must remember, that the voltage on the primary can get quite strongly negative if the VIC is in resonance (it can't get a high positive voltage, due to the freewheeling diode). So this voltage would somehow have to be clamped. Surely the CDs do have internal clamping diodes, but I'm not sure if they could withstand this amount of current, as there's only a quite small resistor in series.
So either the green thing, which looks like a capacitor is a capacitor and is just filtering the input a bit, or it is a varistor. In the first case, the CDs internal diode would have to clamp the signal, but the signal is filtered. in the other case the varistor would do the clamping, but there wouldn't be a filtering.
It's also to mention that this workaround is not really very proper, as it can in some circumstances yield quite some problems in the working of the comparator, as the voltage on the primary could also have some higher harmonics. If he really did it because of the delay, then an usual delay network would probably have been the better solution.
Edit3:
As I thought again about it, I came to the conclusion that it's most probably is a capacitor. For if he really wanted to clamp it additionally he would've taken a diode.
Edit4:
After having some more time to look at the VIC-PCB and do some power-routing coloring I finally realized, that there was no layout mistake. I just thought this at first, but it misled me, that Stan used to wire the gating signal over the connection port and not directly on the PCB. But not to have to wire it externally it seems, that he decided to wire it directly on the PCB by the blue wire.
I'm still asking myself, where exactly the red wire is connected (the one which is connected to the RC-Damper which is the input for the comparator). But it's now past midnight...I will look again at it tomorrow.
If anyone is interested, this is my "modified" version of the VIC-PCB-pic. I take no responsibility for any errors
(especially the power routing around the driving circuit and the analog voltage is a bit weird, there could well be some errors in my pic, and overall the coloring of the power routing is not yet complete!)
(http://img824.imageshack.us/img824/9059/meyerspics69powerroutin.jpg)
