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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.

Posted February 19th, 2014.

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Laying the foundation for a Photo Booth…

The latest project I’be been working on is a powered photo booth, powered by Linux running on an embedded ARM processor. More on that and that later…

I bought two 19″ TVs for the purpose, one for inside the booth and one for outside. The outside one is to present a running slide show of all the photo taken at the venue, along with some prompts to grab a prop and pose for one.

For that purpose, I bought an HDMI stick powered by a Freescale i.MX6Q quad-core ARM processor, the Zealz GK802. It ships with a recent version of Android that’s loaded on an internal microSD card. Not being much of a programmer in general or Android in specific, I found some instructions on the net for loading the stick with other flavors of Linux. Since I had already cloned an Ubuntu 12.04 LTS system I put together on a Freescale i.MX6Q Sabre SD board, I loaded that onto the stick following the multi-boot directions here.

Success! The stick booted and since it was a cloned system, all the remote access components I added  and configured worked straight away. It won’t need a mouse or a keyboard attached because everything can be remotely controlled through the network. It will just run the slide show endlessly using eog (Eye of Gnome), unless a better randomized, looping slide show application can be found.

The image files will be added into the stick remotely as they’re taken. Current plans are to attach a QR code to each image so that those posing can immediately find and download the images to their smart phone. Dispense with the printer and deliver the tiled up and original images through a local wireless network. I’ve not seen any other photo booth vendors or software that offer that.

Posted January 3rd, 2014.

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Yet another little board…

I successfully made and tested another board based on the QFN32 version of the KL25Z device, the smallest package it comes in. It’s a pain to solder down because the PCB pads need to be pre-wet with solder, a generous helping of flux applied, aligned via eye-ball, and then hot air gently blown so as to melt and reflow the solder. A soldering iron top is too fat to get down into the crevasse to solder.


The schematic of the board is here:


The Eagle files and fabrication output are zipped up here: MicroKL25Z-DIP

Three boards may be ordered for $4.25 here: http://oshpark.com/shared_projects/MsCRJIem

Posted October 28th, 2013.


New board for prototyping the functions of the Swiss Photoknife…

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.

Posted October 16th, 2013.

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More Printed Circuit boards…

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

Posted September 25th, 2013.

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