Retro Gadgets: I Swear Officer, I Was Listening To 45

May 9, 2023 by Al Williams 15 Comments

Audio in cars has a long history. Car radios in the 1920s were bulky and expensive. In the 1930s, there was the Motorola radio. They were still expensive — a $540 car with a $130 radio — but much more compact and usable. There were also 8-tracks, cassettes, CDs, and lately digital audio on storage media or streamed over the phone network. There were also record players. For a brief period between 1955 and 1961, you could get a car with a record player. As you might expect, though, they weren’t just any record players. After all, the first thing to break on a car from that era was the mechanical clock. Record players would need to be rugged to work and continue to work in a moving vehicle. As you might also expect, it didn’t work out very well.

It all started with Peter Goldmark, the head of CBS Laboratories. He knew a lot about record players and had been behind the LP — microgroove records that played for 22 minutes on a side at 33.3 RPM instead of 5 minutes on a side at 78 RPM. He knew that a car record player needed to be smaller and shock-resistant. Of course, in those days, it would have tubes, but that could hardly be helped.

The problem turned into one of size. A standard 10- or 12-inch disk is too big to easily fit in the car. A 45 RPM record would be more manageable, but who wants to change the record every three or four minutes while driving?

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Moisture Duck Gives You A Green Thumb

May 9, 2023 by Al Williams 19 Comments

Around the Hackaday bunker, any plant other than a cactus has a real chance of expiring due to thirst. Perhaps we should build some of [MakersFunDuck]’s Moisture Duck boards. As you can see in the video below, the simple PCB with an ATtiny13A tells you when it is time to water the plants. The video also covers several exotic methods of determining the watering status, some of which are pretty complex.

The board is simple because the operation of the device is simple. A fixed resistor creates a voltage divider with the soil, and dry soil has higher resistance than moist soil. A pot sets a threshold, and the microcontroller measures the voltages.

Of course, if you can’t remember to water the plants, you probably can’t remember to change batteries either. So the device sleeps most of the time, and only wakes up every eight seconds to conserve battery. It would be nice to alarm on a low battery, and, honestly, we would probably have made the sleep time longer.

The video covers how he minimizes corrosion, but we aren’t sure how well the board will survive in damp soil, but with a little protection, it might last a while. Besides that, you could probably just consider them almost disposable.

If you are really lazy, you can also automate the actual watering. You can even build that into a smart flower pot.

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A Tale Of Two Pulse Modulators

May 8, 2023 by Al Williams 7 Comments

In the realm of test equipment, there are a number of items that you don’t know you need until you need one. That’s probably the case with the HP11720A pulse modulator. [Tom] acquired two of these even though, by his own admission, he had “no need for these things.” We’d like to say we don’t get that, but — alas — we do.

The good news, though, is he used one of them to measure the quality of some coax cable and shared the exercise with us in the post and a video, which you can watch below. The device can generate pulses with extremely fast rise and fall times (under 10 nanoseconds) at frequencies from 2 to 18 GHz. These were often used in pulsed radar applications and probably cost quite a bit more new than [Tom] shelled out for them.

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A Literate Assembly Language

May 8, 2023 by Al Williams 80 Comments

A recent edition of [Babbage’s] The Chip Letter discusses the obscurity of assembly language. He points out, and I think correctly, that assembly language is more often read than written, yet nearly all of them are hampered by obscurity left over from the days when punched cards had 80 columns and a six-letter symbol was all you could manage in the limited memory space of the computer. For example, without looking it up, what does the ARM instruction FJCVTZS do? The instruction’s full name is Floating-point Javascript Convert to Signed Fixed-point Rounding Towards Zero. Not super helpful.

But it did occur to me that nothing is stopping you from writing a literate assembler that is made to be easier to read. First, most C compilers will accept some sort of asm statement, and you could probably manage that with compile-time string construction and macros. However, I think there is a better possibility.

Reuse, Recycle

Since I sometimes develop new CPU architectures, I have a universal cross assembler that is, honestly, an ugly hack, but it works quite well. I’ve talked about it before, but if you don’t want to read the whole post about it, it uses some simple tricks to convert standard-looking assembly language formats into C code that is then compiled. Executing the resulting program outputs the desired machine language into a desired file format. It is very easy to set up, and in the middle, there’s a nice C program that emits machine code. It is not much more readable than the raw assembly, but you shouldn’t have to see it. But what if we started the process there and made the format readable?

At the heart of the system is a C program that lives in soloasm.c. It handles command line options and output file generation. It calls an external function, genasm with a single integer argument. When that argument is set to 1, it indicates the assembler is in its first pass, and you only need to fill in label values with real numbers. If the pass is a 2, it means actually fill in the array that holds the code.

That array is defined in the __solo_info instruction (soloasm.h). It includes the size of the memory, a pointer to the code, the processor’s word size, the beginning and end addresses, and an error flag. Normally, the system converts your assembly language input into a bunch of function calls it writes inside the genasm function. But in this case, I want to reuse soloasm.c to create a literate assembly language. Continue reading “A Literate Assembly Language” →

The Bicycle (and More) Explained

May 8, 2023 by Al Williams 25 Comments

They say a picture is worth a thousand words, but an animation, then, must be worth a million. Make that animation interactive, and… well, we don’t know how many words it is worth, but it is plenty! That’s the idea behind [Bartosz Ciechanowski’s] blog where he uses clever interactive animations to explain the surprisingly complex physics of riding a bicycle.

The first animation lets you view a rider from any angle and control the rider’s pose. Later ones show you how forces act on the rider and bicycle, starting with example wooden boxes and working back up to the original bike rider with force vectors visible. As you move the rider or the bike, the arrows show you the direction and magnitude of force.

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DIY Metal Detector

May 7, 2023 by Al Williams 19 Comments

If you want to get rich by hunting with a metal detector, you might want to consider how much you invested in the hardware to start with. Finding a tin can with a $200 detector might not make economic sense. But building a metal detector yourself doesn’t have to be hard, as [Mirko] shows in a recent post. His STM32-based pulse induction metal detector looks good and works well, as you can see in the video below.

[Mirko] reports that the device can detect a coin at 30 cm and a large metal object at more than 80 cm. The project uses the Arduino IDE and a Blue Pill STM32 module. The project looks good with an LED module and a rotary encoder to set sensitivity.

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Linux Fu: Supercharge Bash History

May 5, 2023 by Al Williams 18 Comments

Having a history of shell commands is a great idea. It is, of course, enormously handy when you have to run something repetitively or you make a simple mistake that needs correction. However, as I’ve mentioned in the past, bash history isn’t without its problems. For one thing, by default, you don’t get history in one window from typing in another window. If you use a terminal multiplexer or a GUI, you are very likely to have many shells open. You can make them share history, but that comes with its own baggage. If you think about it, we have super fast computers with tons of storage compared to the “old days,” yet shell history is pretty much the same as it has been for decades. But [Rcaloras] did think about it and created Bashhub, a history database for bash, zsh, and probably some other shells, too.

You might think you don’t need anything more than what you have, and, of course, you don’t. However, Bashhub offers privately stored and encrypted history across machines. It also provides context about commands you’ve executed in the past. In other words, you can see the directory you were in, the exact time and date, the system you were on, and the last return code of the command.

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