Failed to get this digital clock kit working :(

[Joseph Noci 1Participant @josephnoci1]

Posted by SillyOldDuffer on 09/05/2021 17:07:21:

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!

[Anonymous]

Posted by SillyOldDuffer on 09/05/2021 17:07:21:

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.

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.

[Mike PooleParticipant @mikepoole82104]

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

[AJAXParticipant @ajax]

Posted by Mike Poole on 09/05/2021 19:00:56:

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.

[AJAXParticipant @ajax]

Posted by Peter Greene on 09/05/2021 18:49:39:

Posted by SillyOldDuffer on 09/05/2021 17:07:21:

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.

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

[AJAXParticipant @ajax]

Posted by SillyOldDuffer on 08/05/2021 16:52:23:

Reading the reviews I see a few people complain about board quality – tracks lifting off with heat, and broken tracks that had to be bridged. Check the tracks carefully with the microscope and for continuity with a multimeter, or – much better an oscilloscope, see below.

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

[Anonymous]

Posted by AJAX on 09/05/2021 19:18:50:

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

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.

[peak4Participant @peak4]

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Joseph Noci 1 on 09/05/2021 17:48:21:

Posted by SillyOldDuffer on 09/05/2021 17:07:21:

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!

.

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.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by peak4 on 09/05/2021 21:04:39:

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

.

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

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by AJAX on 09/05/2021 19:23:00:

Posted by SillyOldDuffer on 08/05/2021 16:52:23:

Reading the reviews I see a few people complain about board quality – tracks lifting off with heat, and broken tracks that had to be bridged. Check the tracks carefully with the microscope and for continuity with a multimeter, or – much better an oscilloscope, see below.

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

.

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Joseph Noci 1 on 09/05/2021 15:34:21:
.

Doubt that R2 orientation is seen by the processor 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…

 

.

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

[Michael GilliganParticipant @michaelgilligan61133]

.

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

[…]

[…]

and nothing interesting happens.

FINIS

[Ian Skeldon 2Participant @ianskeldon2]

Posted by Michael Gilligan on 11/05/2021 17:12:40:

.

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.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ian Skeldon 2 on 11/05/2021 18:18:55:

.

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.

.

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.

[Ian Skeldon 2Participant @ianskeldon2]

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

[duncan webster 1Participant @duncanwebster1]

From the original schematic it appears that the common cathodes are connected to one pin of the chip, so if all 8 segments are lit this pin is required to sink 8* the current of the driver pins. When I've used this type of display there has been a transistor twixt common cathode and chip.

I could well have misread the schematic of course

Edited By duncan webster on 11/05/2021 20:25:02

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for the good thought, Ian

I suspect that the processors may not have been programmed [or are not programmed correctly] but I have no way of checking, and am not much inclined to pursue that side of things.

There were absolutely no instructions, or-logic of-operation, provided with these kits … so not much educational value. … But at least they were very cheap.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 09/05/2021 21:54:50:

[…]

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

…

.

For anyone who might have these ^^^

This appears to be another model from the same series [but lacking the clock colon]

**LINK**

How to Get Your HS420361K-32 4 Digit 7 Segment Display Working with an Arduino

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 11/05/2021 20:50:07:

Thanks for the good thought, Ian

I suspect that the processors may not have been programmed [or are not programmed correctly] but I have no way of checking, and am not much inclined to pursue that side of things.

[…]

.

Nearly to years later … rummaging through my electronics scrap-box, I found the two assembled boards and wondered what, if anything, might be worth salvaging.

Curiosity led me to YouTube, where I found two interesting videos

**LINK**

**LINK**

Case closed

MichaelG.

[Martin KyteParticipant @martinkyte99762]

Can’t you redefine the project as write your own clock code? After all you do have the hardware.

regards Martin

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martin Kyte on 25/02/2023 20:23:01:

Can’t you redefine the project as write your own clock code? After all you do have the hardware.

regards Martin

.

In a word, No

In several words :

1. I have neither the knowledge to write the code, nor the will to learn how
2. The nice man in the first video offers a download of his code, but anyway
3. I couldn’t justify the additional expense of the programming device

I only posted today for the sake of ‘closure’

MichaelG.

.

P.S.

The kits are still available, silly-cheap on ebay

… just search for AT89C2051 DIY Electronics Kit

No idea if they are still duff though.

Edited By Michael Gilligan on 25/02/2023 21:36:14

[duncan webster 1Participant @duncanwebster1]

Michael, I could lend you the programming device k assuming it's a Pic) but I'd not know how to use it. Mine came with a load of other stuff, and is too good to throw away

[Martin KyteParticipant @martinkyte99762]

Not really a serious suggestion more sort of tongue in cheek.

regards Martin

[Martin KyteParticipant @martinkyte99762]

Posted by duncan webster on 25/02/2023 21:54:24:

Michael, I could lend you the programming device k assuming it's a Pic) but I'd not know how to use it. Mine came with a load of other stuff, and is too good to throw away

If it’s a PicKit programmer you can do in circuit programming and debug with it if you provide the connections on your board. Works with the MPLab development environment freely downloadable from the Microchip Technologies website. Runs on Mac or PC.

regards Martin

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