Planet Arduino

Just before the dawn of the PC era, IBM typewriters reached their technical zenith with the Wheelwriter line. A daisy-wheel printer with interchangeable print heads, memory features, and the beginnings of word processing capabilities, the Wheelwriters never got much time to shine before they were eclipsed by PCs. Wheelwriters are available dirt cheap now, and like many IBM products are very hackable, as shown by this simple Arduino interface to make a Wheelwriter into a printer.

[Chris Gregg] likes playing with typewriters – he even got an old Smith Corona to play [Leroy Anderson]’s The Typewriter – and he’s gotten pretty good with these largely obsolete but lovable electromechanical relics. Interfacing a PC to the Wheelwriter could have been as simple as scrounging up an original interface card for the machine, but those are like hen’s teeth, and besides, where’s the sport in that? So [Chris] hooked a logic analyzer to the well-labeled port that would have connected to the interface card and reverse engineered the somewhat odd serial protocol by banging on keys. The interface he came up with for the Wheelwriter is pretty simple – just a Light Blue Bean Plus and a MOSFET to drive the bus high and low for the correct amount of time. The result is what amounts to an alphanumeric printer, but with a little extra code some dot-matrix graphics are possible too.

Having spent a lot of time reverse engineering serial comms, we can appreciate the amount of work this took to accomplish. Looking to do something similar but don’t have the dough for a logic analyzer? Maybe you can free up $22 and get cracking on a similarly impressive hack.

[via r/arduino]

We often see “logic analyzer” projects which are little more than microcontrollers reading data as fast as they can, sending it to a PC, and then plotting the results. Depending on how fast the microcontroller is, these projects range from adequate to not very useful.

At first glance, [esot.eric’s] logic analyzer project has an AVR in it, so it ought to be on the low end of the scale. Then you look at the specs: 32 channels at 30 megasamples per second. How does that work with an AVR in it?

The answer lies in the selection of components. The analyzer uses a 128MB SDRAM DIMM (like an older PC might use for main memory). That makes sense; the Arduino can’t store much data internally. However, it isn’t the storage capacity that makes this choice critical. It seems [esot.eric] has a way to make the RAM “free run”.

The idea is to use the Arduino (or other host microcontroller) to set up the memory. Some of the memory’s output bits feedback to the address and data lines. Then the microcontroller steps aside and the SDRAM clocks samples into its memory by itself at the prevailing clock rate for the memory.

Of course, this isn’t good for things like complex triggering, and you give up some memory storage to the control “program” (if that’s the right word). However, it is easy to see this technique being useful in other cases where you want to offload the CPU for repetitive data transfer. For example, [esot.eric] has also used this method to drive an LCD panel.

Just to prove the point, the video below shows the device working even after the AVR microcontroller is removed. It is only necessary during the setup phase. Admittedly, the logic analyzer part isn’t the cool part. If you want a logic analyzer, pick up a DSLogic from the Hackaday store or one of the many other inexpensive ones out there. If you want to roll your own, there are plenty of options for that, too.

But for sheer audacity and dirty trickery, you have to admire how this design uses an SDRAM in a unique way. It makes you wonder what other components we could use in strange ways.

Bob Davis has built an Arduino powered three Million samples per second six channel logic analyzer:

In the video below you can see what the live display looks like. He is using a 74 series decade counter to divide down a 10Mhz crystal so that he has some nice fast stuff to sample. He experimented with the coding style and found that by being a bit verbose with the instructions he was able to speed up the data collection by over 50%. This technique requires a bit more code space and doesn’t look as elegant as a nice tight loop but execution efficiency is the name of the game here.

[via]

Arduino Uno 3 million samples per second logic analyzer - [Link]

[Reza's] methodical investigation of this remote controlled outlet let him patch in with an Arduino using a 433 MHz transmitter. This is a single-device unit, but the techniques used here should allow you to take control of wireless rigs that have multiple modules to control many devices.

We’ve seen some folks at our local hackerspace try to patch into the remote control itself. That used some type of weird button scanning (not just connecting a pin to ground or voltage) and didn’t pan out. [Reza] doesn’t even crack open the case of either of the units seen above. Instead, he goes straight for a wireless receiver he had on hand, using a logic analyzer to capture the signals coming from the remote.

Once he had a good snapshot of the signals sent when pressing the on or off button of the remote he set out to replicate it in his Arduino code. His function called setStateWithDelay takes three parameters: the transmit pin, the level (high or low), and a number of milliseconds to delay. Each signal calls this function many times, but working the bugs out is pretty easy; just capture the signal with the logic sniffer and compare to the stock remote.