The boards from the previous post finally arrived.
Here’s a photo of the board with the KL25Z mounted along with a few passive components to make it work. The five wires on the left go over to a FRDM-KL25Z board, which supplies power and permits programming the device.
All the pins wiggle as they should, so now the various functions of the Swiss Photoknife can be tested before rolling them all up into a single kitchen sink board…
[UPDATE 10/22/2013] This board has been shared and can be ordered via OSH Park at a slightly higher cost than Seeed Studio.
I became very excited after having received a Freescale smart car kit. Although I have yet to get the camera mounted and make it follow a line, I have been playing with the microcontroller board that came with it, and the online IDE/compiler tool chain for it.
So excited that I just had to build my own boards for it…
There are various boards out there for doing various photographic control functions but there are no one-does-nearly-all, kitchen-sin, Swiss army knife, hackable photo controllers to be had. The boards I made will be the test beds for prototyping the various functions I intend to include on a multipurpose photo control board. More on that later as things progress.
The device at the heart of these proto boards is the Freescale Kinetis KL25Z in the 64-pin QFP package. There is a header for a Nordic Semiconductor nRF224L01+ 2.4GHz data transceiver module that’s are commonly available on eBay. There’s also a header for a Nokia 5110 type LCD display and for programming. All the pins are brought out to a hole and a little general purpose prototype area. Total cost for ten boards measuring 50mm x 50mm was $15, where $5 of it was for shipping (the vendor was Seeed Studio, for those interested; they have extremely good prices…).
I received an email this morning that the boards have been shipped back to me. Now the excruciating wait for them to arrive…
Below are the schematic and layout.
Here are the Eagle and Gerber files: MiniKL25Z-64QFP
Here are some behind the scenes photos from the latest art shoot.
In the foreground, there are two PVC panels, each clamped directly to a light stand. Each panel is illuminated by two Norman LH-2 heads connected through a Y cable by a Norman 200B power pack. All the flat artwork was photographed leaning against the podium.
The sculptures were photographed in a light tent assembled from PVC panel pieces (four straight lengths and four lengths with elbows at each end). A piece of black velvety material hangs from the back so as to appear as an infinite black background. This was illuminated by AC powered slave strobes, but not all three were used for every photo – sometimes fewer were used, depending on the piece. They were alo moved around to change where they were aimed.
There were two very heavy sculptures that had to be photographed in place out in the hall, so one panel was used as a reflector (the one on the left) and the other was used as the diffuse light source.
And here is a final image of the other sculpture piece out in the hall way:
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:
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:
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.
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.