Matsui DA-1 DAB Tuner

[mhennessy]

There is a factor that'll potentially change the results - as David pointed out, low dropout regulators use PNP pass transistors, so the base current is derived from ground rather than the incoming supply voltage, which is what happens with regular regulators using NPN Darlington pass transistors. The base current in the latter case simply becomes part of the output current, but with the 2940, et al, the base current is an additional term that wastes energy.

If you look at the datasheet for an "official" LM2940, you'll see that the quiescent current shoots up as the drop-out voltage decreases. In some cases, that can cause the regulators to "waste" as much power as the basic I times (Vin - Vout) calculation would suggest. I first ran into this many years ago when using these to clean up the output of a switched-mode regulator without impacting on efficiency too much, and found that there was a balance to be struck when setting the output voltage of the switched-mode part, prior to the LM2940s. These were the 12V version, so for a given base current, that was 2.4 times the power wasted compared to the 5V regs...

So probably not a big deal here, but if the results differ from expected, that'll most likely be why. I guess the quiescent current might be around 50mA worst-case, but note that when supplying 1 amp, the current is ~140mA!

Cheers,

Mark



PS: I took a look at the datasheet linked in earlier, but I saw several "typos" and other unexpected results. Normally, these "second-sourced" ICs are more similar to the original than this one appears to be. So actual results might vary

[Paul Stenning]

I had a look at the display contrast arrangement this evening. Pin 1 of the display is 0V, pin 2 is 5V and pin 3 is contrast. There is a potential divider across the 5V supply giving about 0.5V on pin 3. I couldn't read the values on the surface mount resistors even with a magnifier!

I linked pin 3 to pin 1 as suggested in an earlier post but it made the contrast worse (character backgrounds darker). So the contrast voltage clearly needs to be higher not lower. I connected a 10K preset between pins 2 and 3, and twiddled for best contrast. This was at about 0.8V on pin 3, and with the preset removed it measured just over 1.5K.

The only resistors I have are vintage radio size and wouldn't fit between the underside of the PCB and the case, but I tacked a 1.5K 2W resistor in place temporarily to prove the point. I have just ordered 10 1.5K 1/8W resistors on eBay for 99p including postage, and will fit one between the display connector pins when they arrive.

I'm sure it would be possible to calculate the existing resistor values from the information here (it sounds like the sort of thing we had to do at college many years ago), but I can't be bothered to think about it!

[Paul Stenning]

Guy's power consumption figures confirm that with the regulated 6V PSU it will save about 0.7W in the unit itself, plus some in the power adaptor. Not a big deal, and certainly not something I'll notice on the electricity bill, but with both parts running a bit cooler it should help with longevity.

The 0.3W difference between standby and on is pathetic, but I guess the DAB module needs to remain powered so it can wake up again, and that's probably the majority of the power. Turning the display backlight off would have helped a bit, but maybe that's not possible with the type of display used while the time and date are displayed. For the price and market I doubt anyone was bothered about it!

[paulsherwin]

A lot of older digiboxes had this pathetic 'standby' performance. Often the firmware just switched the display or status LEDs to indicate 'standby' without doing anything else. Lots of Freeview boxes would continue to produce audio in 'standby', showing that all the DSP circuitry was still running.

[mhennessy]

A decent designer will include a pre-set for the LCD contrast, and the bean counters will do their best to remove it

This display is reflective rather than transmissive, so switching off the backlight is feasible. It'll almost certainly be on pins 15 and 16. Easy enough to try, and if you're really lucky, you might be able to add a transistor and a resistor, driven from a switched rail or a control pin.

That said, blue LED backlights usually take an order of magnitude less current than the older green types, so it probably doesn't make that much difference in practice to the overall current consumption. Rather than current, it might be excess light (e.g. in a bedroom) that prompts me to think about modifying it.

[Paul Stenning]

There's several other standby lights and displays glowing in my lounge, some of them significantly brighter than this display. So no reason to consider a modification.

I doubt there is a standby signal/voltage anywhere outside the DAB module anyway.

Standby probably turns off the tuner which mutes the audio outputs, but keeps the processor running to respond to the remote control and display the time.

[turretslug]

I had toyed with the idea of fitting something like one of those little square cermet trimmers with a knurled conical knob on the opposite side of the display to the remote sensor as a contrast control but in time-honoured fashion never got round to it. The display they used is a particularly disappointing example of a standard format type that can be replaced with a better one for little effort and outlay, I mentioned this in post 17 of this thread from a while back:

https://www.vintage-radio.net/forum/...ad.php?t=91724

but I appreciate that it's probably an unimportant detail for most, I wanted a scrolling programme info display that was quick and easy to read in bright light sat on the dash while driving. One day, I'll incorporate a bright/dim function fed from the lighting circuit.....,

Colin

[Paul Stenning]

That different display certainly makes a big difference - tempting! They are available on eBay for under £3, and I assume any that mention the HD44780 controller and operate from a 5V supply will do the job?

[mhennessy]

Yes, the HD44780 has been an industry standard since the '80s. There are 14 pins for the interface proper, and pins 15 and 16 - if present - are for the backlight. Not all displays had backlights, and some were wired separately (especially if they were electroluminescent).

The backlight is the thing that varies between displays. As I indicated earlier, older green backlights took a lot of current - that's because they consisted of many LED chips distributed behind the panel; operating currents of ~200mA were not unusual. Modern displays might use the much more efficient InGaN LEDs, and so might only require 20mA, give or take (often just one LED). Both types are readily available today, so do check when ordering.

Be warned that many of the very cheap transmissive (dark background) types have terrible viewing angles and response time. The latter is a particular problem with scrolling text.

[turretslug]

I recall working on kit back in the '90's that had fields of warm-running yellow-green LEDs backlighting their LCDs and, yes, while it was more efficient than incandescent lamps, there wasn't exactly a step-change in wattage reduction. Surely they've been more sophisticated than this for a while now, or perhaps "floodlit" types linger for professional/legacy purposes? The replacement type I used has a single green (towards blue, rather than yellow, in colour) LED in an angular, silvered hood at one end of the display- I thought, oh, that'll be hopelessly uneven and dim, serve me right for buying a cheapo one- but in fact it's both bright and (pretty) evenly illuminating for less than 10mA. It's nearly as crisp and clear as dot-matrix VFD, with a good viewing angle, staying defined and contrasty well off-axis. I was agreeably impressed for what was a price-of-a-pint experiment. I guess that as LCDs are both cheap to make and easy/low power to drive, there must have been a lot of effort and investment to overcome their shortcomings over the years. Though I still put them behind VFD and LED in "niceness"!

[mhennessy]

Yes, the old types are very much still available. For example: http://uk.farnell.com/midas/mc21605g...grn/dp/2218947 - this takes around 130mA. I'm guessing these are for professional/industrial use, as you rarely see them in consumer gear these days.

Backlight technology has really moved on recently, thanks to improvements in LCD TVs and monitors. Most of those are edge-lit by a string of white LEDs, and it's worth taking dead ones apart to examine the diffuser. What looks like a simple sheet of perspex is actually micro-textured on one side. Between that and the glass will be one or more layers of similarly "clever" sheets of plastic, in thin sheet form. I've saved a few for DIY projects... So making a tiny display illuminate pretty evenly with just one white/blue/pure green LED is quite feasible these days. And, straying OT for a moment, this technology is used to produce those light panels that are becoming popular now. We've got a few at work fitted instead of standard 600mm recessed fluorescent fittings, and they are pretty good.

I agree that VFDs are much nicer. They aren't exactly energy-efficient either, but are broadly comparable to the older green/yellow backlit LCDs. And you've got a wide range of colours available. Some are available with a HD44780-compatible interface and on-board DC-DC converters so they can run on just +5V. But they're getting harder to find, and can be extremely expensive in small quantities. And of course, they eventually fade. But I like them a lot

[andrewn]

I've also got this DAB receiver and its been in regular use for years. As a previous poster mentioned the power supply casing becomes brittle and mine broke open so I had to stop using it. I used an old multi voltage linear power supply but started to find the signal would break up on random occasions presumably when a neighbour turns on something noisy. I fitted a voltage regulator between the two units and its worked well for ages. I already had it built up from a previous project but its a bit untidy looking!

[Nymrod121]

Excellent. So we can deal with display issues (contrast, colour, LCD vs. VFD etc.) whilst minimising power consumption (cheap, planet-warming, non-regulated linear 'wallwarts' vs. efficient, relatively-well-definable output voltage type SMPS) ...

... just in time for the entire DAB industry to move over to DAB+.

I *love* this forum! (King Canute would have been proud ...)

Best wishes
Guy

[paulsherwin]

It's possible that this chipset is compatible with DAB+, though the high power consumption suggests that it may not be.