Day: January 13, 2022

Pico Does PID

January 13, 2022 by 23 Comments

If you wanted to, say, control a temperature you might think you could just turn on a heater until you reach the desired temperature and then turn the heater off. That sort of works, but it is suboptimal — you’ll tend to overshoot the goal and then as the system cools down, you’ll have to catch up and the result is often a system that oscillates around the desired value but never really settles on the correct temperature. To solve that, you can use a PID — proportional integral derivative — loop and that’s what [veebch] has done with a Rasberry Pi PICO and Micropython.

The idea is to control an output signal based on the amount of difference between the actual temperature and the desired temperature (the proportional error). In addition, the amount is adjusted based on the long term error (integral) and any short term change (the derivative). You can also see a video about using the control loop to make a better sous vide burger, below. Continue reading “Pico Does PID” →

Microwave Sampler Is Like Time Domain Mixer

January 13, 2022 by 17 Comments

[Gregory] is building some microwave gear and wanted to convert a 3.3 GHz signal to a 12 MHz intermediate frequency. You might think of using a mixer, but you’d need a local oscillator of nearly 3.3 GHz which is not only hard to build, but also will be very close to the signal of interest which is not a great idea. Instead, [Gregory] opted for a sampler, which uses an effect you usually try to avoid — aliasing — to allow downconversion with a much smaller local oscillator. You can see the design in the video below.

In the case of converting 3.3 GHz to 12 MHz, the local oscillator is around 100 MHz. How does that work? Watch the video and find out. The final project will triple the 3.3 GHz signal and we presume the 12 MHz downconvert is to easily phase lock the frequency using a PLL (phase-locked loop).

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Soviet-Era Auto Dialler Uses Magnetic Rope Core Memory

January 13, 2022 by 12 Comments

We’ve seen a few interesting magnetic core memories on these fine pages over the years, but we don’t recall seeing too many user programmable magnetic core memory devices. This interesting Russian telephone auto dialer in its day would have been a very useful device, capable of storing and dialing forty user programmable 7-digit numbers. [mikeselectricstuff] tore into one (video, embedded below), and found some very interesting tech. For its era, this is high technology stuff. Older Russian tech has a reputation for incredibly ingenious use of older parts, that can’t be denied. After all, if it works, then there’s no need to change it. But anyway, what’s interesting here is how the designers decided to solve the problem of programming and recalling of numbers, without using a microprocessor, by using discrete logic and core rope memory.

This is the same technology used by the Apollo Guidance Computer, but in a user configurable form, and obviously much smaller storage capacity. The core array consists of seven, four-bit words, one word per telephone digit, which will be read out sequentially bottom to top. The way you program your number is to take your programming wire, insert it into the appropriate hole (one row related to numbers 1-20, the other row is shifted 1-20 for the second bank) and thread it along the cores in a weave type pattern. Along the way, the wire is passed through or bypasses a particular core, depending upon the digit you are coding for. They key for this encoding is written on the device’s lid. At the end, you then need to terminate the wire in the matching top connector, to allow the circuit to be completed.

As far as we can tell, the encoding is a binary sequence, with a special ‘stop’ code to indicate telephone numbers with less than seven digits. We shall leave further analysis to interested parties, and just point you at the Original manufacturer schematics. Enjoy!

Of course we’re not just going to mention rope core memory and the AGC without linking to a fantastic article about the very same, and if that’s wetting your appetite for making a rope core memory, here’s a little thing about that too!

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Ride-on Tracked Vehicle Is A Stout Metal Build

January 13, 2022 by 17 Comments

When we think of tracked vehicles, we normally think of tanks, or perhaps heavy construction machinery. Meanwhile the average member of the public is left out of the fun. [Bob] of [Making Stuff] won’t be one of them, however, having put together a ride-on tracked vehicle for his own enjoyment.

The machine is welded together from plenty of steel, making it more than tough enough to soak up the punishment of off-road duty. The design features four suspended buggy wheels on either side running inside rubber tracks, with a cogged drive wheel at the front. Propulsion is thanks to a 440 cc DuroMax engine good for a full 18 horsepower and 26 ft-lbs of torque, driving the tracks through a differential mounted up front.

The design has one major issue at the moment. The heavy engine is mounted ahead of the front wheel inside the tracks, which means the vehicle wants to nosedive at the slightest provocation. Such an event would be highly uncomfortable for the rider, so mods are needed, either by scooching the engine back a little or pushing the wheels forward.

We look forward to seeing [Bob] fix the issues and get the machine driving soon. We’ve seen other tracked builds before, too – often on the smaller scale. Video after the break.

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Exploring Tesla Model S High Voltage Cabling

January 13, 2022 by 36 Comments

When he’s not busy with his day job as professor of computer and automotive engineering at Weber State University, [John Kelly] is a prolific producer of educational videos. We found his video tracing out the 22+ meters of high voltage cabling in a Tesla Model S (below the break) quite interesting. [John] does warn that his videos are highly detailed and may not be for everyone:

This is not the Disney Channel. If you are looking to be entertained, this is not the channel for you.

We ignored the warning and jumped right in. The “high” voltages in the case of an electric vehicle (EV) like the Model S is approximately 400 volts. Briefly, external input via the charge connector can be single or three phase, 120 or 250 VAC, depending on your region and charging station. This get boosted to a nominal 400 VDC bus that is distributed around the various vehicle systems, including the motors and the battery pack.

Rear Modules

    • Charge receptacle
    • On-board charger module
    • Rapid splitter
    • Rear motor inverter

Front Modules

    • High voltage junction block
    • Cabin air heater
    • DC to DC converter
    • Battery coolant heater
    • Air conditioning compressor
    • Front motor inverter

He goes through each module, showing in detail the power routing and functionality, eventually assembling the whole system spanning two work benches. We liked his dive into the computer-controlled fuse that recently replaced the standard style one, and were impressed with his thorough use of labels.

If you’ve ever been curious about the high voltage distribution of a EV, grab some popcorn and check out this video. Glancing through his dozens of playlists, [John]’s channel would be a good place to visit if you’re interested any topic related to hybrids and electric vehicles, drive trains, and/or transmissions. We’ve written about some Tesla teardowns before, the Model 3 and the Model S battery packs. Have you worked on / hacked the high voltage system in your EV? Let us know in the comments below.

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Remoticon 2021 // Hash Salehi Outsmarts His Smart Meter

January 13, 2022 by 27 Comments

Smart meters form mesh networks among themselves and transmit your usage data all around. Some of them even allow the power company to turn off your power remotely, through the mesh. You might want to know if any of this information is sensitive, or if the power shutdown system has got glaring security flaws and random people could just turn your house off. Hash Salehi has set out to get inside these meters, and luckily for the rest of us, he was kind enough to share his findings during Remoticon 2021. It’s a journey filled with wonderful tidbits about GNU Radio, embedded devices, and running your own power company inside a Faraday cage.

The smart meter in question is deployed by a power company known as Oncor in the Dallas, Texas, area. These particular meters form an extensive mesh network using a ZigBee module onboard that allows them to to pass messages amongst themselves that eventually make their way to a collector or aggregator to be uploaded to a more central location. Hash obtained his parts via everyone’s favorite online auction house and was surprised to see how many parts were available. Then, with parts in hand, he began all the usual reverse engineering tricks: SDR, Faraday cages, flash chip readers, and recreating the schematic. Continue reading “Remoticon 2021 // Hash Salehi Outsmarts His Smart Meter” →

Impedance Matching Revisited

January 13, 2022 by 14 Comments

If you are an old hand at RF design, you probably have a good handle on matching impedance. However, if you are just getting started with RF, [FesZ Electronic]’s latest video series on lossless impedance matching is well worth watching.

Matching is important for several reasons. Maximum power transfer occurs when the source and load impedance match. Also, at RF, mismatched impedance can cause reflections which, again, robs you of useful power. The video covers some math and then moves on to LTSpice to simulate a test circuit. But the part you are really waiting for — the practical circuits — is about 15 minutes in. Since the values you need are often oddball, [FesZ] makes his own adjustable inductors and uses a trimmer capacitor to adjust the actual capacitance value.

This is a big topic, but the first video is a great introduction blending theory, simulation, and hands-on. A great way to get started with a very fundamental RF design skill.

We’ve worked on explaining all this before if you want a second take on it. If you want to understand why mismatched impedance leads to less power delivery, we’ve done that, too.

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