Mechanical Television Kit

Hawes Mechanical Television Archive

by James T. Hawes, AA9DT

Mechanical Television Kit

First look inside the kit box

The MUTR Kit

We build it. What if John Baird brought back the Daily Express kit? Unfortunately, at some 120 years old, Baird is pushing up daisies. As far as we know, he's out of the kit business. But MUTR offers the kit!

A few days before Thanksgiving, we ordered our kit from Middlesex University Teaching Resources Limited (MUTR) in Herts, England. Unfortunately, the family budget dictates that delivery by Space Shuttle is out of the picture. Result: The trip across the pond takes a long time. We waited patiently. Our kit finally arrived about a month later, a few days before Christmas.

• Get your kit at: Middlesex University Teaching Resources (MUTR)

Differences from the Peter Smith Circuit

Microcontroller, etc. I note several differences from the NBTVA club circuit by Peter Smith. Among these are the microcontroller, the 324 op amp and the output LED-drive transistor T1. On the NBTV forum, Dominic Beesley points out the purpose of the microcontroller: It's there to provide a test pattern. Baird would have liked this feature. In his day, though, microcontrollers were somewhat rare.

Resonator. To me, part Q1 looks a lot like a ceramic filter. Thanks to Klaas Roberts for identifying the part. Actually it's a ceramic resonator. Part Q1 serves as the clock crystal for the microcontroller.

The 4046 phase-locked loop sync circuit is similar to what the club uses.

Part	MUTR Kit	Peter Smith
Microcontroller	12F629	None
Resonator*	Q1	None
Op amp 1	1/2 of LM324N	CA3240
Op amp 2	1/4 of LM324N	CA3140
LED Driver, T1	BC548 (BJT)	IRF510 (FET)
Input follower	None	2N3702 (BJT)

*Frequency = (400 Hz * X) ? (Maybe 4 MHz)

Kit Parts

Resistors

Note: All quarter-watt resistors.

Resistor Table
R01—7.5M	R06—1K	R11—20K	R16—22K	R21—10K pot
R02—10K	R07—10K pot	R12—1K	R17—22K	R22—2.2K
R03—10K	R08—180 Ω	R13—100K	R18—100K
R04—30K	R09—390Ω	R14—220K	R19—100K
R05—1K	R10—100Ω	R15—220Ω	R20—4.7K

Capacitors

Capacitor Table
C01—0.1μF, J / 63V, ceramic	C03—0.1μF, J / 63V, ceramic	C05—22µF, electrolytic
C02—100µF, electrolytic	C04—0.1μF, J / 63V, ceramic	C06—0.1μF, J / 63V, ceramic

Main PC Board

My rough sketch of the PC board (top view) appears below. When time allows, I'll post a better sketch.

Semiconductors

Semiconductor Table
PLL: 4046, 14-pin	Quad Op Amp: LM324, 14-pin	PIC: 16F629, 8-pin
T1, NPN Transistor: BC589 (LED drive)	MOSFET: IR542P / IRL530N (Motor drive)	Opto: Might be Optek OPB710

Sync Problems

On my first attempt, I didn't get the sync working. The raster lights, and I see a flipping image. Obviously the sync doesn't work. No adjustment of the brightness and sync pots improved the situation. From reading the forum page on the scanner, I discovered related chronic problems. First, the disc is some sort of floppy plastic material instead of aluminum. I suspect that the disc is that Darvic® (PVC) plastic type that the NBTV club used to sell. My disc is warped. Because the scanner body is open, you can accidentally touch and slow the disc. That's too bad. Holding the scanner peephole up to your eye is the easiest way to see adjustments.

Here are some another forum discussions of the kit...

Kit Forum 1

Kit Forum 2

Kit Forum 3 (incl. Phonovision)

A second sync-related problem is that the distance between the opto sensor and the strobe disc is variable. You must guess how close to get the opto. Supposedly you should get the opto as close as possible. But the disc wiggles. It might be too close at one time and too far at another. Also, if you get the disc too close, the opto will slice through the strobe disc. The printing is only a laser print. Toner smears and powders off rather easily. One forum member is already trying to repair his strobe disc.

Infrared opto. Another guy mentions that the infrared opto responds to ambient light from the nearby screen illumination LED. He made a shield. I intend to try a shield, too. We sometimes eat prepared dinners, and they come in nice plastic containers. Maybe I can make a shield out of a piece of this plastic.

Better Diffuser

Source. I'm also looking for a replacement diffuser. I think that I've found another container that will provide suitable plastic. See Healthy Choice Cafe Steamers.

Unwanted texture. Like the side of some milk containers, the original diffuser has a stippled surface. The stipples degrade picture resolution. I've seen this problem before.

My scratch-built scanner uses real ground glass from American Science & Surplus. Another place to look for a good piece of ground glass is Surplus Shed. Edmund Scientific (now Anchor) used to deal with amateurs, but the current prices indicate that those days are over. I also don't see as many surplus items at Edmund and Anchor.

Photo: Example of prepared dinner with
diffusion plastic container
This type of dinner comes in a diffused plastic container

Suggested Improvements

Iron the diffuser to remove the stipples. My iron isn't the right tool for this job. Since the iron gets too hot, it would easily wreck the diffuser. One test sheet of plastic turned instantly to mush. I recommend a new diffuser. Replace the diffuser with translucent plastic from a prepared dinner. I tried a sheet of plastic from the TV dinner in the photo above. Although it's a little too thick, this plastic works fine. I had to flatten it out, though. I carefully ironed the plastic, but ironing only worked when I shielded the plastic from the iron with paper towels. Under the plastic, a sheet of cardboard protected the ironing board. I don't want plastic on my shirts!	*Inside the dinner package: A diffuser!*
Sync opto. Shield the opto with a piece of opaque plastic from another TV dinner. After I added the shield (more of a fence, actually), the sync began working. To achieve the best fit, I had to trim the plastic a few times. The disc warp made the fit critical. When cutting the fence, be careful! The black dinner trays are Type 1, PETE plastic. This material is brittle. The black plastic tends to snap off in very sharp pieces. The photo (right) shows how I fastened the fence to the new diffuser. I used the original diffuser mounting screws. The new white diffuser is Type 5, PP plastic. This white plastic is soft, and much more workable than the Type-1 plastic.	*The black, plastic "light fence" that I cut from a prepared dinner tray.*
Replace the red LED with a white LED. During adjustments, I watched the mechanical scanner in the dark. The single red super LED is none too bright. Plus it's a ruby red color, instead of the more authentic orange. (On my scratch-built scanner, I've just modified my circuit to accept three super LEDs.) Other builders assert that a white super LED seems much brighter than the red one. Humans do perceive white as being brighter than red, even if the two light sources are equally bright. Sharper, too. On April 9, 2020, I replaced the kit LED with a white one. My new LED was an eBay acquisition. It's a 20 candlepower super LED with a 24-degree viewing angle. For some reason, the pixels seem both sharper and brighter. Incidentally, the red and white LEDs operate at different voltages. Yet the scanner circuit uses a current-source LED driver: The LED voltage (within reason) doesn't matter.	*A white, super LED of the type that I soldered into the circuit.*

Test Patterns

See... Test Patterns from Klaas Robers, PK0KLS.

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