Using an Hitachi Camcorder Eye Piece as Console

Extracted Eye Piece Viewer In this article, we're going to look at the eye-piece that came out of a salvaged 8mm analog camcorder. The picture at left shows the tiny little black and white TV picture tube once it is fully extracted from the camera. See also the related article for using the Hitachi viewfinder LCD.

The connection specific material here should be directly applicable to the following Hitachi models:

  • VM-E535LA
  • VM-E635LA
  • VM-H835LA

But the principles described should be helpful for you to figure out other brands of salvaged equipment.

Determining Connections

The most difficult aspects of this kind of salvage is to determine:

  1. The power supply voltage (and current)
  2. The connection wiring

I was fortunate in finding a PDF service manual online. However, here are a few ideas that might help you determine the connections for your mystery unit:

  1. Try to determine the ground wire first (it is usually the most obvious one). On my unit, you can measure zero ohms between the metal shielded section and the ground connection at the connector. Shields are almost always connected to ground.
  2. Failing that, look for power filter capacitors. The negative terminal will usually be to the ground PCB trace. It should then read zero ohms back to the incoming ground connection.
  3. Next, try to determine the power input. Sometimes the PCB trace for the power input will be much larger than all the rest (that has worked for me on another unit).
  4. If available, use a power supply with current limiting. My Hitachi eye piece unit drew about 120 mA. Otherwise use something like a 9 volt battery that won't supply too much current into a short-circuit situation.
  5. The voltage will be largely determined by the camera's battery. The Hitachi camcorder used a 6 volt battery, allowing up to 7.2 volts for charging. This tells us that the ceiling voltage is about 6 volts.
  6. Don't use wire colour as a guide. On my Hitachi unit, the +, Gnd and video inputs were all brown wire. The yellow wire is a sync output. Don't assume red or yellow means + input.

Once you have a raster showing after a successful power up, you might want to adjust the brightness and contrast controls to more easily see the screen without a signal (these are on side trim pots on my unit). Note also, the screen size and brightness is sensitive to voltage and current of your power supply. So if using a variable power supply, play with this a bit so that you get a nice raster.

To find your video connection, the best way is to usually just scratch different input wires against a ground connection. You should see the video flicker and scratch as you scratch. Avoid just “trying” wires on the Raspberry Pi video out, since the Pi's output may not be as durable for interaction with “output” connections like the Horizontal Sync. Sometimes you may need to experiment with different contrast and brightness settings to get a visible interaction. Another approach that sometimes works is to hold the suspected video input tightly between your finger tips. If the gain is high enough, you should see modulation in the raster from the power line interference.

Hitachi Connections

Connections While the Hitachi PDF service manual documents the connections, it isn't obvious which pin is pin number 1. Pin 2 is the ground wire (brown wire) on my unit. To verify which is pin 2, measure the resistance between it and the shield (the shield can be seen front left in the picture at top of this article).

Pin 4 is +5 volts (also a brown wire). The battery is 6 volts, but the service manual indicates that the eye piece draws from a regulated 5 volt supply. The “5V5” designation in the service manual just means 5V input number 5 (not 5.5 volts).

In this unit, we already know where the video input goes (pin 3, which too is a brown wire). According to the service manual, pin 1 (yellow) is the Horizontal Sync output (I didn't test this).

Hooking up to the Pi

Console display

If using a separate power supply for the Eye Piece Viewer, don't forget to connect a common ground wire between the Raspberry Pi's power and the power supply used.

With the eye piece video hooked up to the Raspberry Pi's video out, you should see some console output on the screen.

In the photo shown, the output is showing correctly. If you have just removed your unit, then it likely had a lens between the screen and the eye, which inverts image. So your first viewing will likely show it inverted and backwards.

Deflection Connections While the Raspberry Pi can be configured to invert the console image, you will likely prefer to fix the eye piece to show correctly instead. This is easily accomplished by reversing the horizontal and vertical deflection wires. These wires go up to the picture tube at the side where the deflection coils are.

The trick of course, is to get the wires belonging to the same pair. The Hitachi connector is shown at right (again it wasn't obvious which was pin 1). Pin 2 can be verified by measuring resistance between it and ground (pin 2 is connected to ground). In this unit's case, the wires are paired at the connector and so it was easy. Simply cut the wires and solder them back together with their partner instead (I used some heat shrink tubing over the solder joints). These wires are small, so it might require some patience!

If you have an unknown unit, you can verify pairs my measuring the resistance of the wires through the deflection coils. A paired wire should read very low in resistance.

Once the deflection coils are reversed, you can see the console print in its uninverted form as the Raspberry Pi boots up. The one casualty of mine was that the PCB needs to be above the picture tube for the display to be right side up. Given it's small size, this should be no hardship when installed in a case of some sort. In the photo above, I have held it up with the “third hand” bench device so that the display shows right side up.

The text is obviously very small for reading, unless you retained the lens in the eye piece. Without the eye piece, you may still find applications where a graphic chart is drawn. When installed in a small box, you may want to just use it as a way to verify that a video signal is being received (no Pi required). The unit could be powered by a 6 volt battery, perhaps with a silicon diode to drop the voltage down by 0.6 volts.

More interesting electronics DIY projects can be found in the new book "Assimilating the Raspberry Pi", by Warren Gay VE3WWG. The link will display more information and allow you to preview the book, including the Table of Contents.

rpi_hitachi_eye.txt · Last modified: 2013/07/20 21:38 by ve3wwg
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