EEVblog #313 – Bus Pirate LCD Debugging

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Published: Tuesday, 17 July 2012

Written by Jon Chandler

As 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.

A Shattering Wine Glass at 10,000 Frames Per Second

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Published: Tuesday, 10 July 2012

Written by Jon Chandler

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.

The Impact of Pullup Resistors

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Published: Thursday, 05 July 2012

Written by Jon Chandler

Pull-Up Resistors I was assembling my sous vide board and I started to wonder about the number of pullup resistors as I was counting them out.  The board has a total of ten pullup resistors.  At what point does the current drain of the pullup resistors become significant?

The basic circuit is shown below.  The following pullups are on the board:

1. /MCLR (10k)
2. I2C SDA and SCL lines (2 resistors, 4.7k)
3. Switches ( 2 x 10k)
4. Option Jumpers (3 x 10k)
5. SSR (10k)
6. One-Wire (4.7k)

Read more: The Impact of Pullup Resistors

Mini-Tip: Hot Air Gun

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Published: Friday, 22 June 2012

Written by Jon Chandler

You may recall that my Hantek DS-3X55 signal generator met with disaster when I was testing out the Sony-Tek o'scope I got at Goodwill when I had a ground issue with my bench power supply.  I ended up shorting the power supply vis the USB ground connection which resulted in no output.

I found a picture of the Handtek internals on the EEV Blog.  The output of the microcontroller has an op-amp buffer chip.  Since everything worked but I had no output signal, my conclusion was that my power supply short had destroyed it.  The signal generator still responded to USB commands and the sync output operated normally which supported this conclusion.  The board is shown below.  A large microcontroller, a few support chips and a lot of empty space.

The output buffer is the SOIC-8 in the center - an LMH6702A, a low distortion opamp.

Read more: Mini-Tip: Hot Air Gun

Hijack - A Unique Interface to IPhone, IPad and other Audio Devices

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Published: Saturday, 09 June 2012

Written by Jon Chandler

In appreciation for my help on the glass buster and other projects, my producer friend gave me a new iPad .  Very generous and appreciated.  This of course opens up a new world of applications and projects and a sudden interest in magazine articles about interfacing to the device.

In the current issue of Nuts&Volts, there is an article about using an iPxxx as a moisture meter for watering plants.  It connects using only the audio port and uses no external power source.  At a quick glance, I guessed they were using the microphone input as a ADC to measure moisture content but a longer look showed there was more to the system than that.

The moisture meter is based on a Project HiJack interface.  This is a fascinating interface developed by Ye-Sheng Kuo, Thomas Schmid and Prabal Dutta at the University of Michigan and was presented at the ISLPED’10 Design Contest.  The paper presented for the contest is very informative and can be found here.   This incredibly cheap interface has two unique features that allow it to be used with many audio devices: 1) It derives power from an audio signal to power the required circuitry and 2) it used audio tones to create a bi-directional interface over the audio path.  One of the driving goals to to create a low-cost interface that could be used with a huge range of sensors in developing countries.  One of the awesome demonstration projects is a 2-lead EKG.

Read more: Hijack - A Unique Interface to IPhone, IPad and other Audio Devices