Crystal oven temperature sensor reads 0.01F resolution

crystal-oven-temperature-sensor

[Scott Harden] continues his work on a high precision crystal oven. Being able to set a precise temperature depends on the ability to measure temperature with precision as well. That’s where this circuit comes in. It’s based around an LM335 linear temperature sensor. He’s designed support circuitry that can read temperature with hundredth-of-a-degree resolution.

Reading the sensor directly with an AVR microcontroller’s Analog-to-Digital Converter (ADC) will only yield about 1-2 degrees of range. He approached the problem by amplifying the output of the sensor to target a specific range. For the demonstration he adjusts the swing from 0-5V to correspond to a room temperature to body temperature range.

Of course he’s using analog circuitry to make this happen. But before our digital-only readers click away you should view his video explanation. This exhibits the base functionality of OpAmps. And we think [Scott] did a great job of presenting the concepts by providing a clear and readable schematic and explaining each part slowly and completely.

So what’s this crystal oven we mentioned? It’s a radio project that goes back several years.

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Weather-O-Matic displays digital weather on an analog face

SANYO DIGITAL CAMERA

This clean-looking readout uses analog dials to display the weather. [Nuno Martins] calls it the Weather-O-Matic and after the jump he explains what went into the project.

The hardware is about as simple as it gets. Each hand has a servo motor attached to it. An MSP430 gets the weather via a serial connection to a computer (data is scraped by a Python script) and sets the dials accordingly. The microcontroller also takes user input in the form of a single button on the side of the frame. The words on the left side of the dial are Portuguese for Today, Tomorrow, and After (meaning the day after tomorrow). Pressing the button multiple times will scroll through these three words, followed by the forecast temperature high and low for that day being displayed.

The nice thing about this is that the servo motors will stay in place if you cut the power to them. We bet if he wanted to make this a permanent fixture in his house he could get it to run well on batteries by using the sleep function of the microcontroller and adding an RF transceiver to communicate with the server.

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Analog input expansion boards for Raspberry Pi

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[Ken Olsen] needed a bunch of analog inputs for his model railroad project. He wanted to use the Raspberry Pi board, but alas there are no analog inputs available on the GPIO header. But there is SPI. So he used an online service to design his on Analog input expansion boards.

He mentions that Eagle can be a bit of a pain to work with. For this project he decided to give circuits.io a try. This is an in-browser PCB layout tool which we looked at in a links post some time ago. The service lets you order directly from your in-browser design without the need to run gerber files or the like (boards are made using the OSH Park service). He’s very happy with the boards he got back. They feature a footprint for a connector to interface with the RPi.

The design uses MCP3008 Analog to SPI chips. Each has eight channels but [Ken] needed more than that. Since the service provides three copies of the board he made them modular by adding end connectors which chain the SPI and power rails from one board to the next. Don’t miss his full demo in the video after the break.

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Retrotechtacular: Donner 3500 portable analog computer

retrotechtacular-donner3500

What if we told you we had a computer you can take with you? What if it only weighed 28 pounds? This is a pretty hard sell when today you can get a 1.5 GHz quad-core processor packing computer to carry in your pocket which weighs less than 5 ounces. But back in the day the Donner 3500 was something to raise an eyebrow at, especially for tinkerers like us.

The machine was unveiled in 1959 as an analog computer. Instead of accepting programs via a terminal, or punch cards, it worked more like a breadboard. The top of the case features a grid of connectors (they look like banana plugs to us but we’re not sure). The kit came with components which the user could plug into the top to make the machine function (or compute) in different ways.

We’re skeptical as to how portable this actually was. It used vacuum tubes which are not fans of being jostled. Still, coming during the days when most computers were taking up entire buildings we guess the marketing claim holds up. If you’d like to see a bit more about the machine’s internals check out this forum post.

GSM to Landline box has a creatively soldered cellphone inside

gsm-to-landline-box-teardown

We don’t blame the manufacturer of this GSM to Landline converter box for not designing the thing from the ground-up. After all, quantities of scale have made dumb-cellphones available for next to nothing. But you have to admit that it’s interesting to see a fully populated cellphone board creatively soldered into a consumer product. It would be commonplace if made in your basement rather than being sold in a store.

[Anton] was using the box to add his analog house phones to the cell network. The signal strength at home is pretty low and this box offers an external antenna for better reception. He cracked open the case expecting to see a GSM modem and was surprised to see the cellphone board. It includes a battery backup, and has been soldered directly to the cables which interface with the main PCB using some SIL connectors. Those solder joints were done by hand directly to the pins of the SIM card slot and as well as all of the other important connection points.

VISUALIST – a hardware visual effects synthesizer

[Berto] wrote in to tell us about the visual effects synthesizer he built. It works as a pass-through for a video signal, rendering crisp clean images into a more psychedelic flavor like the one seen above. On the one hand this does a dishonor to the high-quality video devices we carry around in our pockets these days. On the other hand it will make some really interesting background video at a party or at your local dance club.

This is not a filter for a PC, or an FPGA-based processing system. A set of analog parts alter the incoming composite video (NTSC or PAL formats) and pipes the result to a television or projector. [Berto] included controls to alter the effects. They’re mounted on a panel and everything is given a home inside of a handy carrying case. Check out the video clip after the break to get a better idea of the video manipulations this things can pull off.

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Arduino voltage measurement tricks

We think it’s a great learning experience to tear back the veil of abstraction and learn a bit more about the hardware found on an Arduino board. This project is a great example. [Scott Daniels] takes a look at the other voltage measurement options available to AVR chips used by Arduino.

If you’ve used the analogRead() function then you’ve already measured a voltage using the Arduino. But do you know what is going on behind the scenes to make this happen? The Analog to Digital converter on the AVR chip is being used to measure an incoming voltage by comparing it to a known voltage reference. That reference is by default the supply voltage line for the chip. This should be 5V but will only be as accurate as the regulator supplying it. [Scott] looks at the other voltage references that may be used. An external reference can be used by adding hardware, but that’s not the focus of his article. Instead he looks at using the 1.1V internal reference. He’s written some short example code that let’s you measure the incoming line voltage based on that internal reference. This is a very handy trick that can let you detect when the chips is running from a battery and how much juice is left in the cell.

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