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LED vintage watch on a breadboard with AT90S8535 and DS1302

_._ 5451 9

TL;DR

  • Breadboard LED vintage watch à la 90s uses an AT90S8535 microcontroller and a DS1302 RTC.
  • The AT90S8535 gets and sets time from the DS1302, then drives a multiplexed display with a 1 ms timer interrupt and 200 µs segment lighting.
  • The build uses an 8 MHz quartz, and uploading a 4 kB program takes almost 6 minutes with a USBASP programmer.
  • The finished watch has found a place of honor on the shelf and shows the time.
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  • Design "for fun", vintage watch à la 90s, made on a contact plate. A gadget perfect for the shelf. :)

    I had an AT90S8535 controller in stock, and since I recently returned to programming, I decided to use it for something useful. The once exorbitant 8 kB of flash on board is rather different from today`s standards, and it is so slow that uploading a 4 kB program takes almost 6 minutes using the USBASP programmer.

    DIY 90s-style clock on a breadboard with an LED display. Breadboard with electronic components forming a 90s-style vintage clock. Electronic schematic of a retro-style clock on a breadboard.

    The construction is quite standard. The controller`s task is to get/set the time from the RTC clock (DS1302) and control the multiplexed display. The control is based on a timer that generates an interrupt every 1 ms with an 8 MHz quartz. The interrupt procedure turns off and on the next segment and keeps the light on for 200 µs. The main loop deals with data retrieval, button and beeper control.

    Basically, I made the project as a training and reminder of AVR programming in C, while the assembly on a breadboard involves a bit of modeling to make it work and look good. :)

    The watch has found a place of honor on the shelf and does its job - it shows the time. ;)

    Cool? Ranking DIY
    About Author
    _._
    Level 11  
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    _._ wrote 46 posts with rating 247. Been with us since 2013 year.
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  • #2 20941206
    efi222
    Level 22  
    Posts: 763
    Help: 12
    Rate: 1199
    I wonder how long this watch will work without failure on the contact board. Congratulations on installing this system :)
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  • #3 20941293
    MikeC
    Level 32  
    Posts: 1391
    Help: 201
    Rate: 970
    _._ wrote:
    Design "for fun", vintage watch à la 90s

    In the 1990s, contact sheets were not used, they used universal ones.
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  • #4 20941488
    maliniak80
    Level 17  
    Posts: 287
    Help: 2
    Rate: 377
    Nevertheless, it would be better to solder it even on a universal machine, and if it is "vintage", add some period elements if they are to be visible, e.g. this DS would look nice here:

    Black Dallas DS12887 integrated circuit with visible pins.
  • #5 20942076
    SuMariok
    Level 9  
    Posts: 39
    Rate: 18
    If electronics can look nice, it`s probably in this form. These colorful cables seem to be doing the job here.
    Just three things. It would be necessary to lay these cables from the transistors to the display cathodes on the substrate/board and add a photosensitive element to control the brightness of the LEDs under the lighting,
    and cover it in some plexiglass to protect it. To prevent corrosion of the contacts, you can spray some technical Vaseline. and enclose it in plexiglass :)

    maliniak80 wrote:
    This DS would look nice here:

    If these clocks were, for example, pistachio and not black, it would be perfect, but it would spoil the picture.
  • #6 20942396
    gulson
    System Administrator  
    Posts: 29367
    Help: 148
    Rate: 6050
    I personally like it on the breadboard and respect it for cramming it onto the breadboard :) It is aesthetically made, that`s the most important thing.
    Write to me at Paczkomat and I will send you a small gift.
  • #7 20945526
    rb401
    Level 39  
    Posts: 3002
    Help: 750
    Rate: 984
    _._ wrote:
    however, mounting on a breadboard involves a bit of modeling to make it work and look good :)


    The atmosphere is there, at least when it comes to appearance. But like other colleagues here, I have some concerns about the reliability of structures using this technology in the long term.

    Therefore, for information, I would like to mention that there are interesting boards that allow you to "consolidate" such a project with little effort, rearranging the elements and connections exactly as they are and soldering them:

    Set of Perma-Proto prototype boards on AliExpress page.

    https://www.aliexpress.com/item/4000372753001.html

    I just bought them from this Chinese company and I can say that these boards are made very carefully (e.g. gold-plated soldering points), you can choose from a variety of colors, and using them is pleasant. And it saves time, compared to, for example, transferring a concept proven on a contact sheet to a normal universal PCB. And the price is acceptable.
    As a side note to this digression, this is a minor problem, because while the "half" contact sheets match exactly those PCBs (30 columns here and there), there is a discrepancy in the case of long contact sheets. Contact sheets (at least the ones I have) have 64 columns and PCB ones only have 60.
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  • #8 20953278
    jarekgol
    Level 40  
    Posts: 5147
    Help: 642
    Rate: 1137
    @_._ what is the deviation from the synchronized time over a month/year? From what I remember, the ISP programmer on LPT did not take so long to load these programs.
  • #9 20962745
    _._
    Level 11  
    Posts: 46
    Rate: 247
    It hasn`t worked for that long, but it has already made a difference of a few seconds, so it`s probably not the most accurate, but it`s still pleasing to the eye.
  • #10 21012904
    arrakiszexelon
    Level 1  
    Posts: 1
    >>20940542

    Where does somebody obtain the code to operate the -- AT90S8535 -- in this clock mode?

    And... what does it take to program the AT90S8535 so it works like the breadboard does? If I were to build this, I would just design a PCB.
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Topic summary

✨ A user designed a vintage-style watch using an AT90S8535 microcontroller and a DS1302 real-time clock (RTC) on a breadboard, aiming for a nostalgic aesthetic reminiscent of the 1990s. The project involves controlling a multiplexed display with a timer interrupt for segment activation. Responses from the community express concerns about the reliability of breadboard constructions over time, suggesting soldering components onto a universal PCB for durability. Some users recommend enhancing the design with protective elements like plexiglass and photosensitive components for LED brightness control. Additionally, inquiries were made about programming the AT90S8535 and sourcing the necessary code for the clock functionality.
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FAQ

TL;DR: With an 8 MHz crystal and a 1 ms interrupt, this "aesthetically made" AT90S8535 + DS1302 breadboard clock shows hobbyists how to build a working vintage LED shelf display from old AVR parts, while exposing the main trade-off: strong visual appeal versus weaker long-term reliability than soldered construction. [#20940542]

Why it matters: It helps AVR hobbyists reuse legacy parts, prototype a clock fast, and judge when a breadboard build should become a soldered one.

Option Assembly method Main advantage Main drawback Specific thread detail
Breadboard Solderless contact board Fast prototyping and strong visual style Long-term contact reliability questioned Finished clock stayed on a shelf as a display piece
Universal PCB Soldered board Better permanence Less immediate, less playful build style Commenters said 1990s DIY builds more often used universal boards
Breadboard-matching solder PCB Soldered, layout-preserving board Keeps nearly the same placement and wiring Size mismatch can appear Long breadboards may have 64 columns, while matching PCBs may have 60

Key insight: The project succeeds because it is simple: an AT90S8535 reads a DS1302 RTC and multiplexes the LED display. The thread’s real lesson is that presentation can justify a breadboard, but durability still favors soldered hardware.

Quick Facts

  • The controller used was an AT90S8535 with 8 kB flash, which the author framed as large by old standards but tiny today. [#20940542]
  • The clock ran from an 8 MHz crystal, and the firmware used a timer interrupt every 1 ms. [#20940542]
  • In each interrupt cycle, the code switched to the next display segment and kept it lit for 200 µs to implement multiplexing. [#20940542]
  • Uploading a 4 kB program with a USBASP programmer took almost 6 minutes, showing how slow this setup felt on the older AVR. [#20940542]
  • The author reported a drift of a few seconds over the initial test period, so timekeeping was visually acceptable but not precision-grade. [#20962745]

How was the LED vintage watch on a breadboard built around the AT90S8535 and DS1302 step by step?

It was built by combining an AT90S8535, a DS1302 RTC, and a multiplexed LED display on a contact board. 1. Place the AVR, DS1302, display, transistors, buttons, and beeper on the breadboard. 2. Run the AVR from an 8 MHz crystal and write firmware with a 1 ms timer interrupt. 3. Use the main loop to read or set time from the DS1302 and handle buttons and the beeper while the interrupt refreshes the display. [#20940542]

What is a contact board in electronics, and how does it differ from a universal soldered PCB?

A contact board is a solderless prototyping board that holds parts by spring contacts, allowing quick wiring changes without soldering. In this thread, it was valued for aesthetics and fast assembly, but several commenters questioned long-term reliability. A universal PCB differs because you solder parts permanently, which usually improves durability and better matches how many 1990s DIY builds were actually made. [#20941293]

Where can I get the code for running an AT90S8535 as a clock controller in this kind of LED watch?

The thread does not provide the code or a download link for the AT90S8535 clock firmware. One later commenter explicitly asked where to obtain code for running the AT90S8535 in this clock mode, which confirms that the source was not published in the shown discussion. To reproduce this build exactly, you would need the original author to share the firmware separately. [#21012904]

What hardware and software do I need to program an AT90S8535 so it works like this breadboard clock?

You need an AT90S8535-based target circuit, a programmer such as USBASP, and firmware written for the clock’s hardware. The thread states that the author used USBASP and programmed the AVR in C after returning to AVR development. The target hardware also includes an 8 MHz crystal, a DS1302 RTC, the multiplexed LED display, buttons, and a beeper because the firmware controls all of them. [#20940542]

Why does uploading a 4 kB program to the AT90S8535 with USBASP take almost 6 minutes, and how can that be sped up?

It is slow in this setup because the author observed that writing a 4 kB program with USBASP took almost 6 minutes on this older AVR workflow. The thread does not give a tuning method or fuse setting that fixes it. It only adds a comparison: one commenter remembered LPT-based ISP programming as faster, so changing programmer setup or workflow may help, but no tested speed-up is documented here. [#20953278]

What is the DS1302 RTC, and what role does it play in an AVR clock project?

"DS1302" is a real-time clock chip that keeps calendar time independently of the main microcontroller, providing a dedicated time source for display projects. In this build, the AT90S8535 gets and sets time through the DS1302, while separate code handles LED multiplexing, buttons, and the beeper. That division keeps timekeeping logic distinct from display refresh logic. [#20940542]

How does multiplexing the LED display with a 1 ms timer interrupt and 200 µs segment on-time work in practice?

It works by refreshing one display section at a time fast enough that the whole display appears continuously lit. The firmware uses a timer interrupt every 1 ms with an 8 MHz crystal. In each interrupt, it turns one segment off, enables the next segment, and leaves it on for 200 µs. The main loop then stays free for time reads, button handling, and beeper control. [#20940542]

Breadboard vs universal PCB for a vintage LED clock build: which is better for long-term reliability and appearance?

A breadboard is better for appearance and experimentation here, while a universal PCB is better for long-term reliability. Multiple commenters praised the breadboard build as attractive and carefully arranged, but several also warned about durability over time. One commenter called it “aesthetically made,” while others recommended soldering it on a universal board if permanence mattered more than display style. [#20942396]

What kind of time drift should I expect from a DS1302-based clock over a month or a year, and how can I improve its accuracy?

This thread only documents a short test, and the observed drift was already a few seconds. That means you should expect noticeable accumulation over longer periods if you leave the design unchanged. The discussion does not give a calibrated monthly or yearly figure, and it does not describe a correction routine, so the practical answer is to measure your own assembled clock against synchronized time before treating it as accurate. [#20962745]

Which alternatives to the DS1302 would be better if I want a more accurate RTC in an AVR watch project?

The thread does not name any RTC alternatives, so it cannot support a chip-for-chip recommendation. What it does show is the motivation for looking: the DS1302-based build had already drifted by a few seconds during the early test period. If accuracy is your priority, this discussion only justifies searching for a replacement; it does not identify one. [#20962745]

How should I add automatic LED brightness control with a photosensor to an AT90S8535 clock?

The thread suggests adding a photosensitive element so LED brightness follows ambient light, but it does not include a schematic, pin assignment, or code. The idea appears as a practical improvement alongside cleaner wiring and a plexiglass cover. In other words, the concept is clearly endorsed, but implementation details for the AT90S8535 are absent from the discussion you have here. [#20942076]

What are the best ways to protect a breadboard clock from contact corrosion, dust, and accidental damage?

The thread recommends three simple protections: cover the build with plexiglass, use technical Vaseline on contacts, and avoid exposed wire runs where possible. One commenter suggested plexiglass twice, which shows that mechanical protection mattered as much as appearance. Those steps target the main breadboard risks: dust, accidental touch damage, and contact degradation over time. [#20942076]

Why were 1990s DIY electronic clocks more often built on universal boards instead of modern solderless breadboards?

They were more often built on universal boards because that was the typical permanent construction method cited in the discussion. One commenter directly corrected the “1990s” framing by saying contact boards were not what people used then; universal boards were. That matters if you want true period style rather than a modern retro look built on a present-day solderless breadboard. [#20941293]

How do I move a working breadboard prototype to a PCB that preserves the same layout and wiring as closely as possible?

Use a breadboard-matching solder PCB that lets you keep nearly the same element placement and interconnect pattern. 1. Keep the validated breadboard layout. 2. Transfer parts to a matching solder PCB column by column. 3. Recreate the same wiring and solder it permanently. A commenter noted that this approach saves time compared with redrawing the project onto a normal universal PCB. [#20945526]

What compatibility issues should I watch for when using breadboard-matching solder PCBs, especially the 64-column vs 60-column size difference?

Watch the column count before buying, because long boards may not match exactly. The thread reports that some long contact boards have 64 columns, while the matching solder PCBs discussed have only 60. “Half” breadboards fit those PCBs exactly, but longer layouts can overrun the board by 4 columns, which can break a one-to-one transfer plan. [#20945526]
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