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Listing contents with tag DIY:

HP LaserJet 1000-series continuously feeds paper.

2024-03-23 22:00:12,  In: DIY, Electronics

This happened to my old LaserJet 1005, but will happen to any printer of this line, as this (not to confuse with types starting with P or M, these are totally different printers!) is one of the last decent HP laser printers. The first symptom is that the printer, instead of feeding the paper once, does it twice. It means that you cannot use auto-feeder and have to feed every page separately, but it still works.
Then, it starts to repeat the paper feed cycle three times. Quickly three becomes four, and when it becomes around five, then the printer stops with error. If you try to feed the paper then, it may even work, depending on time passed - you then have to make it try to feed the paper by quickly putting paper back and forth, and when it resets to the "ready to feed" state, you put the paper and it prints.
Or, in extreme cases, it will still repeat the paper feed cycle and, when paper is fed, will pass it thru without printing. But if you wait, you hear a metalic cling from the right side of the...

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A TV Tennis game description

2019-08-24 21:17:37,  In: Electronics, DIY

The device, a TV Tennis game, has been made using designs from different sources, especially a description in "Radioamator" and images of the prototype. The general rule is similar to "Odyssey" but the signal mixing is simplified while still giving TV-friendly signals. There are only NPN signal transistors and 74 chips, to be exact one 7474 dual flipflop, 7473 as divider and 7493 as additional divider. Other chips are 7400, in many possible configurations. All other things like delays or integrations are made using discrete components. If someone wants to build a similar unit, prepare for a long tuning and selection of components.
This is a general view of the device. It has a power switch, 1/2 player switch and speed setting. Two controllers consist of X/Y pots, serve and "Lift" buttons which changes deflection...

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Expanding Arduino UNO memory with 32kB static RAM chip

2018-07-04 17:42:04,  In: DIY, Electronics

Arduino Uno is a cheap microcontroller platform which can be used in lots of applications. If we prototype our solution using Arduino board, it is possible to dump the Arduino board and use single microcontroller instead which is even cheaper and looks more professional even on an universal solder-in PCB. However, ATMega328 chip used in Uno has a significant drawback - its memory which is only 2kB. If we want to make a small control device it's not a problem, but for some specific applications 2kB may be too small.
For example, since few weeks I have an idea to develop a BASIC computer using AVR chips. Implementation of Tiny BASIC uses some memory and has some code clutter which can be replaced with something more usable by the cost of e.g. moving storage code to external devices. Unfortunately Tiny BASIC leaves a very small memory for user's program and its variables.

So what are options to add RAM into Arduino?
- Use a larger Arduino module. This solution is present in Internet forums all...

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Re-making a gear for tape memory

2017-09-24 01:47:52,  In: DIY, Electronics

A long time ago I acquired a microcomputer-grade tape recorder produced by Polish factory: MK-450. The problem with this device and a few other tape drives (like Mera one for large cassettes) and even consumer-grade decks (MK-250) was a poor quality of its gears prone to breakage. Usually, during seeking or playback, a loud crack is heard and tape is pulled into recorder or forward seeking stops working while motor is still heard. Recently I got a possibility to print something with 3D printer, so I decided to experiment with it. In this post I'll show how to re-produce the existing, physical gear into computer model. To quickly show things, the result is nice:

   But... why does it fail?

The plastic used to make these two specific gears (in MK450) is different than polymer used in other gears. It degrades into white, crumbling powder with atmospheric contact and probably...

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A hole in the casing

2017-01-30 20:50:00,  In: DIY, Retrocomputing

Sometimes old computers come with broken plastic parts. When only cracks are present, it's easy - we can fix them with glue or staples melted into plastic using soldering iron. Even totally broken casing can be fixed this way. The bigger problem is when the casing lacks some part which cracked off. Recently I purchased an old computer with broken front panel. From photos it can be seen that damages aren't so big and two parts can be glued together, but if you look closer you will notice that a whole bottom-left corner of panel is missing. How to fix it?

I decided to try with hot-melt glue applied from pistol-type hot glue applicator. First, I found that front panel is made of porous, well-glueable plastic, so I glued broken parts together using cyanoacrylic glue. I found that this panel is painted with something similar to white acrylic paint. Next, I started to apply hot-melt glue to form a patch. The key factor here is temperature. The glue comes from the gun very hot. When hot, the glue is liquid...

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Programming PICs with Willem Programmer

2016-08-31 22:52:31,  In: DIY, Electronics

After replacing laser I needed a Modchip for my 20-year-old PS1 console. Following the "DIY" principle I downloaded an archive from with dumps of MultiMode 3 mod chip for PIC12F629. It contains even source code! I obtained a blank PIC chip and tried to program it in Willem programmer PCB v. 3. Of course Willem has no support for them. But it is still possible to write to the chip.
The first rule when programming PICs in Willem is to avoid Willem software. It is not well prepared for programming PICs. First of all, PICs have not only configuration bits (like AVR's Fusebits), but also factory-configured last 16-bit word called OSCCAL word. This word is used to calibrate internal RC oscillator and is set separately for each chip in factory, where RC characteristics are verified against real timing. So to program a PIC, you have to read it first, get OSCCAL value and program a new dump with old value good for the particular chip you have in programmer. It's really easy to erase OSCCAL with Willem...

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Making a professional-looking stickers

2016-08-01 16:43:38,  In: Hack, DIY

Again I got an old computer with a sticker missing. This is quite frequent, especially in machines which were used in schools - everyone wanted to have a piece of computer and stickers were stolen in the beginning. If the sticker was molded using non-flat form, then there is a problem as they are not easily made at home (but still possible using e.g. silicone forms and polymer resins). But if the problem is a flat sticker, it can be made very simple way. You need:

1. 1:1 scale print-out of the sticker.
2. Transparent sticky tape
3. Two-sided sticky tape. Do not use foam tapes, use flat ones. You can find it in home improvement stores as tape for fixing carpets or doormats.
So first of all, print the sticker proper way. Use a good vector graphics program like Inkscape to make your sticker, as it allows to get the true scale of the image, lossless rescaling of vector graphics and its CMYK has black. If you put a black-background bitmap on black-background vector, you will get two black colors: From...

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