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Mic Mono/Stereo Adapter, PCB version…

A previous post detailed an adapter that could combine two mono mics with 1/8″ jacks for use with a camcorder, as well as a headphone splitter so that two headphones can be used with a single jack on a camcorder.

This adapter was used to record a video.  A Rode VideoMic on a boom pole and an Audio Technica ATR-3350 clipped on the talent were used together with the mic combiner part of this design. The boom pole operator and the camera operator both had headphones on using the splitter part.

A board has now been designed that can function as either a mono/stereo combiner or headphone splitter depending on how the jumpers are configured. The board is set up so that 0.1″ headers can be used with computer type jumper blocks but the configuration can be soldered in place as well.

Here is the schematic:


The Mic Adapter configuration has three modes of operation:

  1. Two mono mics are combined from jacks J1 and J2 to J5.
  2. A stereo mic can be plugged into J1 with stereo output at J5.
  3. A single mono mic can be plugged into J2 and appears as a stereo mic at J5.

In the headphone configuration, a stereo source may plugged into any jack and two headphones into the remaining two jacks. It should be noted that in this configuration, J1 always needs to have something plugged in to keep the left and right channels from being shorted together. (This could have been avoided but it would have required extra jumper points. Boards made with the existing design can have the trace cut at J1 if this is a concern.)

The layout is here:


Boards may be ordered at OSH Park. It uses these jacks (from Digikey).

The board offers no strain relief, so care must be taken to keep the jacks from being pulled off the board.

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Norman 200B Low Voltage Sync Mod – details…

Finally, the details of the modification of the Norman 200B for low voltage sync…

DISCLAIMER: The high voltage inside a Norman 200B can be lethal. Never measure with bare meter probes; use something like these Pamona test clips. Always allow the capacitors inside the 200B to discharge by turning the power switch to the off position for a long time. Perform this modification at your own and your equipment’s risk.

Here is a partial schematic of the controller board:

200B LowV Mod schematic

The SYNC connection goes out to the head and test switch. With the components shown, the SYNC voltage is somewhere around 100V. I have seen several controller boards with two 33k Ohm resistors in place of R1 and R2. These boards have a SYNC voltage of around 30V. Note that the case of t he 200B is positive (+BATT) and that the SYNC connection is negative relative to the case.

The TRIG connection also goes to the head. It sits at around -400V. The voltage charges the trigger capacitor in the head. When the SCR fires, it shorts the capacitor across the trigger coil which then fires the flash tube.

As drawn, the SYNC side of the diode is slightly more negative than the R2 side, which is around -80V. In the steady state, capacitor C1 (0.02uF) has about 320V across it. When the SYNC terminal is shorted to +BATT, C1 temporarily acts as a short circuit, pulling the gate of the SCR positive and causing it to fire, triggering the flash tube.

In order to convert the SYNC connection to a lower voltage, the values of R1 and R2 need to be lowered to reduce the voltage. To get about 12V at the SYNC connection, the resistances should be changed so that R1 is 120k and R2 is slightly lower, say 100k. The resistors can be replaced altogether or appropriately sized resistors can be piggy-backed onto the existing ones to yield the equivalent parallel resistance.

When the divided voltage is lowered, though, the flash will no longer reliably fire. This happens because when SYNC is shorted to +BATT, the positive spike on the SCR gate is smaller because the voltage across C1 increases when SYNC is made smaller. To correct this, the capacitance of C1 and the resistance of R3 both need to be increased. I found that adding a 0.1uF @ 500V capacitor in parallel with C1 and replacing R3 with a 330 Ohm resistor worked well to keep the current in the SYNC line when first shorted and then held about the same as with all the original component values.

Now, here’s a photo with the components labeled:

200B LowV Mod board

If a SYNC voltage lower than about 12V is desired, then the resistors dividers will need to be changed accordingly. Then R3 and C1 may also need to be adjusted for reliably triggering the flash.

Please forgive me for not actually inserting photos of the modification itself – if I wait until I get a chance to take them, this will never get posted… Please also forgive me for not giving real explicit details; the reason is twofold: 1) If you know what you’re doing, you can figure it out and 2) I’ve seen component value variations in the 8-10 boards I’ve touched which makes providing explicit details somewhat pointless.

The next project is to replace the analog logic performed by the op amps (which really should been comparators instead of op amps, but I digress…) with a microcontroller board that monitors the SYNC connection, triggers the flash, and controls the capacitor recharging. Using the microcontroller allows watching for pre-flash pulses used by Nikon CLS/AWL, which then allows the 200B to be remotely controlled.  If I get really ambitious,  I can kludge a way for the micro to control the power but that’s very much less trivial given the high voltages and currents in the capacitor/flash tube path.

Stay tuned…


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Multiple exposures…

I shot another art show for an the online version of the reality. It also serves as an archive of all the artwork that’s been shown since the beginning.

One of the pieces in the most recent show was this neon piece that’s close to 5 feet  in width and height. Here is the final image I ended up with after doing three separate masking layers. It was the most challenging piece in this show.


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Updated Norman 200B low voltage trigger…

**** UPDATE *****



A recent previous post detailed the first and second passes at converting Norman 200B strobe packs to low voltage so as to be compatible with modern cameras. Those were not quite up to snuff because the first pass stole too much voltage to be usable and the second allowed 20mA of current to flow through the camera or trigger it was connected to.

After doing some reading about the subject, it would appear that at least for some older cameras, the trigger circuitry used an SCR, in which case the 2nd implementation above would fail because the constant 20mA would keep the SCR latched on. It might also be way too much current for the trigger circuitry to handle. The numbers I recall were 1.5mA max trigger current that decayed to something under 750uA.

So, back to the drawing board… Here’s what I came up with:

Norman Low-V Adapter4
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DIY Kubota Panels: Versatile and Portable Walls or Windows…

During the presentation Kevin Kubota gave on CreativeLive.com several months back, he mentioned DIY scrims he had built that were sized to fitPhotoflex Litepanel covers. He even made a video detailing the construction.

So, how could I help myself? I had to make some, but with some enhancements of my own…

Not having any Photoflex panels, I was not constrained to a certain size so kept things simple. I maximized the material usage by cutting all the 3/4″ PVC pipe to 39″ in length. I also used electrical PVC conduit because it was slightly cheaper than the same size plumbing PVC pipe. Instead of using a hack saw like Kevin Kubota, I used a PVC pipe cutter. They are much simpler to use and so much less messy than sawing – I highly recommend getting one. It’s definitely worth the money.

Seven lengths of pipe are required for each panel. Instead of running bungie cord through them, I opted to leave them separate. I just glued the elbows and Tees to all the horizontal pipes. This lets me know which joints come apart without having to mark anything. It also prevents the loss of any of the fittings while in transit or during storage. Additionally, no bungie means the panel pieces can be configured into a light tent using four end pieces (elbows) and four plain lengths of pipe, similar to the one detailed in this blog post.

One panel breaks down into these pieces:


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