Failed to get this digital clock kit working :(

It is reprogrammable FLASH chip - I am very familiar with it, extended Intel 8051 type device - did MANY projects with most of the 8051 variants , in assembler and C.. I have all the compliers and assemblers too...And the 'big advantage of the arduino platform' is no less complicated than any other method, until you know how...

But all that is moot, since unless someone can do it for Michael, I am sure he is not interested in getting down low with the code!

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Thanks, Joe ... I have an update :

1. I rigged some better lighting on the stereo microscope, and have confirmed that R2 is inserted the wrong way round.
2. I have confirmed that both the processor and its socket are correctly orientated.
3. I have confirmed that all solder joints are ‘sound’ and there are no accidental bridges.
4. I have confirmed that pin 10 of the processor is at Gnd, and pin 20 at VCC 1 [VCC minus the diode forward voltage drop]
5. and I have dug out my ‘Timer Counter’ and checked the oscillator, which is running at 12000.3KHz
6. There is still nothing on the display

Despite your previous reassurance; is there any chance that the mis-orientation of R2 could be completely blanking the display ? ... Could it be a ‘feature’ of the [totally undocumented program] ?

Please don’t waste too much of your time on a silly little project that cost less than £1.50 though !!

MichaelG.

Doubt that R2 orientation is seen by the processor at all..

here is a crude representation of whats going on -

The processor drives open collector ( probably FETs, so open drain, but irrelevant here) transistor as shown. eight drive the A-G and D.P. segments of the displays.

4 drive the scan lines DS1-4

having looked more carefully at your schematic there is a qick test to see if the segment glow at all..will explain shortly.

So, assume VCC at pin 1 of the resistor network, ie, assume the network is inserted correctly..

Then current will flow down R1 (diagram below) through the 7 segment LED, IF the scan line transistor is on.

So, to turn on Segment 1 of display 1 ( say), as below, the A-G line transistor ( top one) must be OFF, and the scan line transistor ( bottom one) must be ON.

to turn a segment OFF, the processor will drive the top transistor ON, which pulls the the LED/R2 network pin to GND, so no current available to flow through the LED, so no glow.

Now, if you connected VCC to pin 9 instead of pin 1, then current still flows down R1, through the segment LED and the bottom transistor, BUT, it gets there via R8. Since R1 thru R8 are equal values ( 470ohm), half the current now will flow through the led, so half as bright. No other effects at all..

Now the test -

Remove the processor from the socket, power the board, and with a wire jumper, short one of the DS lines to GND. That should light up ALL the segment of one of the digits. Repeat for the others. You van see how that works - current can flow through all the segments since the top transistor is OFF ( missing), so shorting the DS1-4 line to GND provides the current flow path.

If NO segments glow, the display is faulty, or as I have had before, its a common anode instead of common cathode device...

Have you checked S1 and S2 are correctly inserted? If those switches are inserted 90° out, the switch inside is bypassed, and the circuit is permanently ON.

The operating instructions explain the program goes into menu mode by a detecting a long press on S1. If S1 is stuck in a permanent long press due to the component being physically rotated, the computer may be waiting for it to be released. As the long press never ends because the switch is shorted, could well be the program doesn't get to move on to a stage where something is displayed.

T0 should be +5 when unpressed and 0V when pressed. If T0 or T1 is permanently 0V, suspect the switches.

Dave

Probably the most sensible of all our rantings!

Is that how they work? Pretty poor design of switch then with pins at the corners of a square and no apparent keying, physical or visual.

I'd have assumed they were spst with all 4 contacts shorted when pressed and open-circuit when released .... but I don't know for sure.

The switches are not quite square but at 6mm x 6.5mm they are close, the components on my effort are all correctly oriented but it doesn’t work. As it cost me very little I am struggling to generate the enthusiasm to investigate the problem.

Mike

Mike, I sketched this for you - I hope it helps.

Bear in mind that even a "failed project" is not a waste of time. It's all a learning experience.

The switches are square, but the pin layout is not. It's therefore generally difficult to place them incorrectly in a PCB.

Tracks lifting off with heat - sounds like a typical problem with beginner soldering to me.

Yes, it looked square on first glance at the board but I see now they're not.

OTOH if, as Mike says, the difference in pin spacing between sides is only .5mm in 6mm, I would think it would be easy enough to install 90-deg out as SOD said.

Michael, Not commenting on faulting this circuit, but I do note you saying that your scope is in storage.

If you have a variac, it might be worth powering up your scope slowly to give a bit of time for the capacitors to re-form.

Bill

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Dave and Joe

Yes that’s a excellent observation [which I note has been addressed by Mike, but I’m trying to keep some chronology] ... and it deserves an honest and detailed answer:

I realised that it could be a problem, but happily found that the switches are not quite square ... they fit easily in one orientation, so I presumed that to be by design.

Checking my decision against the Amazon listing that I posted earlier ... My switches are orientated the same as in their picture.

I have not actually checked which way they work, but I feel confident.

Thanks also for the operating instructions !

... I note that they are for a different board, but hopefully any differences are only cosmetic.

MichaelG.

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Fair point, Bill ... but it’s a little Tektronix digital, so [hopefully] should be better behaved than the traditional ones.

MichaelG.

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The board appears fine to me ... the only problem was that some of the holes are a little oversize for the leads that they accept; which might result in the unwary applying their iron for too long.

MichaelG

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Thanks for yet more helpful guidance, Joe ... it’s appreciated.

I wish I had seen your comment about the R2 orientation before I tried to remove it

My solder sucker needs a new [and preferably smaller] tip for work like this ... so I resorted to ‘wick’

After two hours [on nine pins !] I gave it up as a bad job ... most of the solder is removed, but R2 is still hanging on tight.

I tried the simplified display test, and yes ... some elements of some digits light up [and the sounder beeps]

Incidentally, the display is marked HS20401K-30 but I have yet to find its data-sheet.

All things considered ... I think I will just build the second kit and see how it goes.

MichaelG.

Edited By Michael Gilligan on 09/05/2021 21:55:30

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Chapter 2 ... in which the second kit is built very carefully

[…]

[…]

and nothing interesting happens.

FINIS

Well done, isn't it funny how some problems that could easily be ignored just eat away you and you have to find the answers.

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The answer being that however carefully I build them ... they don’t work

Final result is that I have two boards from which I will reclaim the displays sometime.

... but at least I’ve had some soldering practice.

... and, being retired, I don’t need to put a price on my time

MichaelG.

My apologies Michael, I thought you meant that your second one was working!