A new 90-line Mirror Screw

[acl]

tc2 (1).asm

(25.85 KiB) Downloaded 77 times

World User Manual 2.3.pdf

(531.55 KiB) Downloaded 71 times

Manuel.pdf

(495.44 KiB) Downloaded 78 times

[Steve Anderson]

I'm sure it works as advertised, but DIN plugs? No thanks, as reliable as the British summer. Why the Germans came up with this I have no idea. Assuming it was them. Give me a 9-pin D-type anyday! DIN connectors are cheao and it shows. The same can be said of SCART, nice idea, shame about the reliablity.

Sorry for the rant, but it's my experiance...give me a BNC, XLR or D-type anyday! Thankfully DIN or SCART connectors are virtually unknown in Asia, even if the gear in your house might have them. My old S-VHS VCR had SCART I/O but was never used. It also had Y/C in and out on 4-pin mini DINs, getting cables for that wasn't easy!!

Steve A.

I'll get back on-topic soon...

[Harry Dalek]

I'm sure it works as advertised, but DIN plugs? No thanks, as reliable as the British summer. Why the Germans came up with this I have no idea.

The BEST vengeance is to succeed the Germans are not stupid !

[Panrock]

At Slat 61 now.

Talk about a boring job! Each slat's active edge has to be given an individual final polish, and the other edges' blacking 'topped up' with a marker pen. These will be looked at again when all the slats are in situ and the mirror screw fully assembled. At least it's beginning to look like a real mirror screw now!

It would be nice to house this televisor in a veneered cabinet. Anybody got some photos of the TeKaDe originals to hand?

Steve O

[Panrock]

Today, all 90 slats are now mounted, the whole stack squeezed between collars, and the top bearing and its board - mounted. By some fluke it all fits together surprisingly well... remember this televisor has been built from 'junk' found lying around... e.g. the lower bearings and carrier once were part of my colour Nipkow 30-line camera. This project has been co-operative so far and seems to 'want to be built'.

Next, I'll spin the screw up and see what its balance is like. And whether the motor is powerful enough to reach 25 Hz.

Steve O

[Harry Dalek]

Looks like another beautiful mirror screw evolving Steve .

[Panrock]

Thank you Harry. We can always rely on you to say something nice.

Meanwhile, here it is as it is at present, lying on its back.

I've given it a first run-up, to a relatively slow speed. The balance is critically determined by the correct 'screw expanse' of the slats... ie. they must not quite describe a full circle. Or at least that's how I understand it.

It's now clear there is no question the motor will have the gumption to achieve or exceed 25 rotations per second.

The next thing will be to make a gently graduated power supply for the motor (it's currently running from a 'step' type home-made bench supply). Then it just needs to run within 7% of the correct speed - and the WC-01 will frame-sync to it. A 2N3055 with heat sink comes to mind, driven as an emitter follower, with the base current controlled by a pot, as speed control... that's what I've always done before.

Steve O

[Panrock]

Actually, I'd forgotten that I usually have to put another emitter-follower stage in between the 2N3055 and the pot, using something like a BD135. This allows me to use a commonplace on/off volume control as the on/off speed control (controlling several amps).

I see I've no longer got any 2N3055's in stock, so while I wait for them, I'll jot out the circuit. This won't appear here until I've built it and finalised the values (for this motor and mechanical load).

Incidentally, I understand this motor was originally from the heater fan in a Lada. Up to the job of keeping its owner warm in Siberia!

Steve O

[Steve Anderson]

It might have been worth considering something like a NPN Darlington Power Transistor (TIP142) instead of the 2N3055/BD135 combination, one device, single-hole mounting, in-built Emitter-Base resistors, and back-EMF diode. But if you've already ordered the '3055s, no big issue. The usual suppliers (RS/Farnell) stock both the NPN TIP142 & PNP TIP147.

The attatched datasheet also covers the PNP version (TIP147).

Thinking further, a power MOSFET maybe worth considering too....near zero gate current....

Steve A.

TIP142.pdf

(135.35 KiB) Downloaded 42 times

[Panrock]

Great advice there... thank you!

I have done the cutting and drilling now for a sub-assembly to take the components (and obtained a 2N3055) so we'll try it this way first. Picture to follow when it's wired up.

Steve O

[Steve Anderson]

In both cases I mentioned above I would also add a 'catch diode' across the motor, simply to be sure that back-EMF isn't going to destroy the active device(s). Belt and braces as ever....it is probably a cheap messy DC brushed motor after all...

Steve A.

[Panrock]

Yes Steve, I already had such a diode planned.

However, I live off 1N4007's (and 1N4148's) here. Would a 1N4007 be fast enough? Or should something else like a small C be added, to finish the job?

Steve O

[Steve Anderson]

The Farnell/Element14 order code 3639217 seems ideal. As the motor is somewhat of an unknown I'd rather over-specify the device. I would try without a cap unless some interference shows up, the motor may already have one internally if the car had an AM radio fitted. (probable).

Check the diode pinning info, it's 'different'/unusual...at least to me...the 'tab' is also internally connected. It probably won't need a heatsink.

But try a 1N400x device first...If a cap (if needed) try an X-rated (240V AC) device as a start. Say 100nF? But be prepared for maybe 1uF...

Steve A.

[Panrock]

The Farnell/Element14 order code 3639217 seems ideal.

Wow! No messing. I wouldn't want to be a voltage spike being caught by that. Maybe it's also stocked by RS... I could then get one on a regular order.

Otherwise things are proceeding steadily. You wouldn't think just suppling a varying voltage to a DC motor would involve days of work, but there you have it. As I say, picture to come.

Steve O

[Steve Anderson]

Maybe it's also stocked by RS... Steve O

I had a quick look at RS, no exact same part, but many very similar....I prefer the local (Thai) Element 14/Farnell website only because I find their website far easier to use than the RS one. The parts are in local currency and delivered from Singapore, generally next day.

On the few occasions I have used the local RS website, prices and delivery are much the same.

For the more common/standard components I use two local (i.e. in Bangkok) distributors, just a short Skytrain ride away. I send them a 'shopping list', and when I get there it's ready waiting for me. They do deliver, but I enjoy wandering around that area, many 'oddities' can be found and/or 'things that might come in useful'. Think of a middle-east market, a souk, much like that, except all electronic stuff.

Steve A.