RTL-SDR as Oregon Scientific sensor sniffer

Many Oregon Scientific do not have any PC interface (they are present in WMR200 or I-900 but usally not available in cheaper ones). Their radio sensors transmit on 433.92 MHz sending data packets containing the data every 30 seconds using OOK and manchester encoding for 32 bits of data.
Kevin Mehall wrote Python script that decodes radio signal trasmitted by Oregon Scientific and captured with RTL-SDR (DVB-T tuner working as SDR hardware).

Precise DIY LC + ESR meter with ATmega88

This DIY meter allows pretty precise measurement of inductance (10 nH - 100 H), capacitance (1 pF - 100 mF) and low resistances or ESR (5 mOhm - 30 Ohm).

You can find project documentation or buy componets as a kit on dr. Le Hung site.

Dual-channel USB oscilloscope/recorder

This simple USB oscilloscope allows continuous data recording at 2x300 kSps, 8 bit. Although it has very reduced analog part (low input impedance, no gain switch, only single 0-6.6V measurement range) it could be worlds third cheapest dual channel oscilloscope (right after sound card and this AVR circuit). It is based on STM32F103C8T6 - Cortex M3 microcontroller with Full-Speed USB costing around $4.
PCB dimensions: 66 x 36 mm, total cost 8 - 10 USD.
It works with miniscope v4 PC software:

Updated (2012.04.29) firmware makes use of both A/D converters allowing to increase input impedance (no crosstalk between channels). Sampling speed is increased to 2x461 kSps and S/H time is increased from 7.5 cycles to 13.5 cycles.

ADCs can still work faster, but this is most likely maximum speed that can be handled by USB full-speed and real time streaming is most important feature here allowing to use i.e. 2x128 k sample buffer with MCU that has much less RAM and store to file continuous stream up to 10^9 samples (limited by used file format). While this circuit can not by any means compete with bench oscilloscopes in sampling speed category it can beat even expensive ones in terms of sampling buffer size using up to 4 GB of disk space to capture waveform. 

STM32 F0 series seminars in North America

From ST: "STM32 F0 microcontrollers are sampling now at the resale price of $0.95 for quantities of 1000 pieces to lead customers. Full production is scheduled for the beginning of Q2 2012, and the devices will be available in 32-pin UFQFPN32, 48-pin LQFP48 and 64-pin LQFP64 package options with 20-pin and 100-pin extensions soon to follow."
Same as when introducing Cortex-M3 or F4 microcontrollers, ST Microelectronics is organizing educational seminars - currently scheduled in North America in May and June. Free STM32 F0 Discovery Kit is on the menu. Dates and locations:

16.05.2012		Vancouver
17.05.2012		Seattle
22.05.2012		Santa Clara
22.05.2012		Cleveland
24.05.2012		Dallas
29.05.2012		Montreal
31.05.2012		Toronto
5.06.2012		Atlanta
5.06.2012		Chicago
7.06.2012		Minneapolis
7.06.2012		Orlando
12.06.2012		Orange County
14.06.2012		San Diego
19.06.2012		Boston
21.06.2012		Philadelphia
28.06.2012		Phoenix

Retro electronics: recording in stereo with acoustic head model

One more clipping from '70s magazine "Юный Техник". Article describes stereo recording technique using acoustic human head model with attached microphones - whole idea is pretty clean explained by picture. According to it this method results in very precise spatial reproduction when listening to records. The drawback is that these records should be listened using headphones.

Retro electronics: sleeping stimulator

Another interesting clipping from '70s magazine "Юный Техник". This article describes device that is supposed to help with sleeping by generating regular audible pulses (60...90 Hz). It might be actually early predecessor of SITA. According to this article desired pulse frequency might be related to heartbeat.

Solar battery made from transistors

This is little solar battery I've made from few power transistors about 20 years ago (that's why transistors are little rusty).

There is one piece of 2N3055 (third from the left), four HOTs (some of them were already damaged before cutting the case - I've got them as damaged from TV service, but they still worked with no problems as solar cells) and most interesting - KT801A, medium power transistor from USSR with enormously large when comparing to case silicon area (fifth).

The unusual thing is that it's die has irregular shape - I suppose this transistor was hand-assembled. Even with some remains of protecting paint on it this transistor worked better than others.

The idea is even older - I've spotted it first in magazines "Zrób to sam" ("DIY") from late '70s or early '80s and "Юный Техник" ("Young Technician").


"Zrób to sam" - solar powered AM radio receiver:

 

"Юный Техник" - solar (and wind) powered scarecrow. It's solar battery is actually made of diodes (40-60 pieces) with glass packages.

 

eZ430-Chronos promotion

This week eZ430-Chronos kit is offered at half the normal price at tideals.com. Kit includes waterproof MSP430-based watch and two USB dongles: programmer/debugger and RF access point. Free shipping.

STM32F4DISCOVERY - cheap STM32F4 board

Farnell is currently selling STM32F4DISCOVERY board at a very low price, $16 per piece. Let's compare this with individual cost of components on the board:

• STM32F407VGT6 (MCU): $9.29 (directly from STM, with 1000 pcs quantity),
• LIS302DL (accelerometer): $6.8 (Farnell, no price info on STM pages),
• MP45DT02 (MEMS microphone): $2.87 (Farnell, 500+ quantity),
• CS43L22 (DAC): $3.12 (Mouser, 100 pcs),
• STM32F103C8T6 (another MCU working as USB to SWD bridge, on-board ST-LINK/V2 debugger interface):  $3.1 (STM, 1000 pcs),
• ... and PCB and bunch of discrete parts.

It definitely looks that STM is not making money with this board but sells it as a promotional product to popularize STM32F4 series microcontrollers. If you are interested in this family in particular or if you need relatively high-performance platform for audio processing this would be great buy. On the other hand this is kind of "bait and switch" offer as STM32F407VGT6 in small quantities has similar price to the whole development board. Other drawback (comparing to older STM32F103 board) is that ST-LINK part can not be detached by splitting PCB into two pieces.

AVR DDS signal generator

AVR-only (with no specialized DDS chip and no DAC chip) DDS generator from scienceprog.com seems to be valuable addition to hobbyist workshop. Its output frequency range is limited to 65 kHz for DDS signals (sine, square, saw, rev saw, triangle, ECG, noise) but that seems sufficient for many needs and it allows to use cheap operational amplifier and R-2R digital to analog converter. Additional HS (high speed) digital output would be useful as a spare external clock source for microcontroller projects or restoring misconfigured AVR fusebits.

New project version with improved analog part and some additions to firmware is planned to be released this summer.