What's in an SD card?

sd1What's actually inside an SD card?  I'll bet you've wondered that, but never actually got round to finding out?

I'm sure you've all seen the insides of a USB memory stick - a bunch of chips on a PCB, nothing surprising there.  But what about an SD card?  Considerably slimmer than a USB key they must be going some to fit the chips you'd expect into it.

Well, since the Raspberry Pi handilly blew up an SD card for me, I thought it was about time to rip one apart and see what it's actually made up of.  Well, it contained one or two surprises I must say.  Actually one big surprise.

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Simple Circuit Tests Twisted-Pair Cables - Try 2

An EDN Design Idea - Originally published in the May 29, 1986, issue of EDN

Mark D Braunstein, Contel Information Systems, Fairfax, VA; Edited by Paul Rako and Fran Granville - January 19, 2012

Using the system shown in below, you can quickly test a cable containing twisted-wire pairs and detect open or reversed pairs, shorted pairs, and shorts between unrelated pairs. The tester consists of an active test set that plugs into one end of the cable, and a passive terminator that plugs into the other end. (An RS-449 cable is used as an example.)

EDN Cable Tester
A battery or a dc supply delivers 15 to 24V to the test set. The voltage regulator (IC1) is connected as a current regulator to supply a nominal 25 mA to the LED strings at each end of the cable. The cable in this example contains eight twisted pairs, and for a good cable, all eight LEDs in the test set (DA through DH, which are series-connected segments of a bar-graph display) and all eight LEDs in the terminator (D1 through D8) will light. If a twisted pair is open or reversed, the corresponding LED on the terminator will be extinguished; if a pair is shorted, corresponding LEDs at both ends will be extinguished; and if any two unrelated wires of different pairs are shorted, all intervening LEDs in the strings at both ends will be extinguished. For example, if pins 4 and 6 are shorted, LEDs DA, DB, D1, and D2 will not light.

You can add a heat sink to the IC1 regulator as a safety precaution, but normal tester operation is well within the regulator’s power-dissipation limits. Even with many shorted pairs, a dissipation of 700 mW would cause no more than 60°C junction temperature, and the IC is guaranteed to turn itself off at 160°C. The complete tester costs less than $50 to build.

Simple Circuit Tests Twisted-Pair Cables

This circuit should prove useful to anyone using multi-pair cables.  The idea would work well for an RJ-45 network cable tester.


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Control an LM317T with a PWM signal

An EDN Design Idea

Aruna Prabath Rubasinghe, University of Moratuwa, Moratuwa, Sri Lanka; Edited by Martin Rowe and Fran Granville - February 3, 2011


Control an LM317T with a PWM signal figure 1The LM317T from National Semiconductor is a popular adjustable-voltage regulator that provides output voltages of 1.25 to 37V with maximum 1.5A current. You can adjust the output voltage with a potentiometer. The circuit in Figure 1 replaces the potentiometer with an analog voltage that you can control from a PWM (pulse-width-modulation) signal. You control this signal with a microcontroller or any other digital circuit. You can use the same microcontroller to dynamically monitor the output and adjust the LM317T.

Using an RC lowpass filter and an op amp, you can convert the PWM signal to a dc level that can adjust the LM317T’s voltage output. Varying the pulse width of the input signal lets you generate an analog voltage of 0 to 5V at the output of the lowpass filter. The op amp multiplies the voltage to achieve the desired voltage range.

For scenarios in which you must multiply the input voltage by two, the LM317T’s adjustment pin receives 0 to 10V. Its output-voltage range is 1.25 to 11.25V. The equation VOUT=VADJ+1.25V governs the LM3175T’s output voltage. You can change the op amp’s gain by choosing proper values for R4 and R2. You must be able to remove offset voltages from the op amp. Use an op amp, such as a National Semiconductor LM741, with null adjustment. The selection of values for the capacitor and resistor for the RC lowpass filter depends on the PWM signal’s frequency. This circuit uses values for a 1-kHz PWM signal.

You can improve the circuit by replacing the RC lowpass filter with an active filter and then feeding a feedback signal from the circuit’s output into the microcontroller for dynamic adjustments.

Comments to this article at EDN suggest that the LM741 op amp is not an ideal choice for this circuit; a better choice would be a rail-rail op amp.

 Control an LM317T with a PWM signal

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Wow! A Scientific Calculator From The Dollar Store

teaserYou may have seen the ads for The Dollar Store.  How much is this flower arrangement?  One Dollar.   How much is this tea kettle?  One Dollar.  How much is this package of light bulbs?  ONE DOLLAR.  How much is this 56 function, 10 digit scientific calculator?  ONE DOLLAR.  EVERYTHING IN THE STORE IS ONE DOLLAR.

I'm dating myself to say my first "real calculator" was a Texas Instruments SR-50A, slightly newer than the SR-50 shown here.  It had a price tag of around $170 35 years ago.  Nice red LED display, many functions and a rechargeable battery that would last all day provided I remembered to plug it in.  i had a few moments of panic in college when I had forgetten to recharge the night before a test!


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thumb mramHands up any of you that have heard of MRAM?  That's "Magneto-Resistive Random Access Memory", by the way.

MRAM is set to blow the socks off the microcontroller world, or my name's not Felicity Kendall.  Until recently I didn't even know they were actually commercially making this stuff yet, but it turns out they are.

But, what is Magneto-watsit thingummyjig?  Simply put, it's RAM that uses a magical combination of magnetism and resistance to store data.  Now, I'm not going to even pretend to know how it works, so here's my friend Wikipedia to explain it:

Read more: MRAM Joy

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Site Migration Complete

Just a quick message to let everyone know that the site migration is complete. We are now on SSD hardware and double the processing power.

If you are viewing this message from facebook / twitter / RSS and the link takes you to an offline page then your DNS settings are old. Either wait a few hours or try using Google public DNS.

Enjoy and please report any issues via the feedback page.

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Using Optical Switches

breadboard -300Applying micro controllers to the real world often involves sensing motion, position or the proximity of objects.  A very simple sensor is the optical switch consisting of an IR LED emitter and an IR-sensitive phototransistor.  These can be arranged to detect directly transmitted light (photo interrupter) or the reflection of light (proximity detector) and they can be packaged into a self-contained sensor or used as separate emitter / receivers.  The photo below shows an interrupter type and a proximity detector type that may be purchased for less than a buck a piece.

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DipTrace layout and ordering boards from Dorkbot aka OSH Park

From KuzyaTech

KuzyaTech has a gerat article on producing printed circuit boards at OSH Park using files generated by DipTrace.  Following these recommendations will help ensure you get the boards you expect.

Well, my test design is complete and now I need a few prototypes to play with. The usual ways of ordering PCBs are rather expensive, with just tooling fees in hundreds of dollars. The remaining options are a few China based places, and an OSH Park ran by Laen from Dorkbot. He runs a community PCB service that groups orders and orders them periodically on a common panel, sharing costs between all people. The cost is very reasonable ($5 a square inch) and you get three boards. So a 2″ board in three copies will cost you $10 delivered. That definitely opens the door for quick prototyping of pretty much anything! After having used other company’s prototyping services, I must say OSH is also by far the most user friendly. Lets walk through the steps of ordering these boards.

First you need to check that the design complies with the design rules listed.  Ideally those are setup at the beginning so that you do not have to deal with things being too close or two narrow after the fact. Here is what they look like in DipTrace (Under Verificaton, Design Rules)

Read the entire story


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EEVblog #313 – Bus Pirate LCD Debugging

EEVBlog-304As MrDEB contemplates using another LCD, Dave Jones has created another great video on using Dangerous Protptype's Bus Private for testing an LCD display.  I've mentioned the Bus Pirate here before - it'sa serial analyzer/interface that understands a number of protocols.  If you're trying to figure out an I2C, SPI, UART or One-Wire interface (among others) the Bus Pirate can be a huge asset.

Dangerous Prototypes makes an 74HC595- based converter to go from the serial protocol that the Bus Pirate understands to the parallel interface of a character LCD.  If this sounds at all familiar, it's a technique that been discussed by mrbasher and Mike here extensively in the past.

Dave makes quick work of checking out a 8x2 display with the Bus Pirate.  As with most of Dave's videos, there are lessons to be learned, including the dangers of using dual-row header cables.  Dave had a crossed cable between the Bus Pirate and the '595 adapter board which was quickly found and corrected.  If the cable had been reversed between the '595 adapter and the LCD, the outcome mat have been much worse.

Dave is very good at systematic troubleshooting - watch and learn.

EEVblog #313 – Bus Pirate LCD Debugging


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A Shattering Wine Glass at 10,000 Frames Per Second

Ignore the hype -this video shows a vine glass shattering using the system I built.  Note the incredible deflection before it shatters explosively. 

 Shatter Sessions TV from Creature on Vimeo.

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