2017-02-18

Dr. Vogel's Analog Computer

In 2014 I discovered the Analog Computer Museum and I was intrigued over a small analog computer in the collection. Dr.Vogel's small computer is an educational computer with very limited capabilities, but still it looked like a nice project to replicate.



The schematics for the computer are here, a short introduction to analog computing is here and the documentation of the computer is here.

Well the construction took several years, from the choosing the box, the type of plugs/sockets (2mm instead of the common 4mm), designing the front panel and sending it for fabrication (at this place as they do have linux support, for an idea of how incredibly long it took, the front panel was done in 2014).



At the circuit part, I made some "variations"... for the power supply I wanted a mains input and a linear regulator for each polarity. So I used a standard transformer, rectifier and LM337, LM317 regulator with +15V and -15V outputs.
In the circuit I changed all operational amplifiers for the LF411 and LF412. In the polarity indicator I used a dual colored LED (red/green), with this I could save one extra hole in the front panel. For the sinus generator I got a AD639 as I couldn't afford the space for the pots and diodes. Eventually I got the AD534 for the multiplier, but it appears that the ones remaining in ebay are made of unobtanium...
For the integrators I used pots as input resistors so that I could adjust the time constants.
After sourcing all the components, the construction took two weeks on several pcb pre-drilled boards (one of these, another of these and for the power supply another).

This is the final result:


With the box open you can see the power supply (transformer in white PCB), the measuring card (brown PCB inside the box, contains basically the second page of the schematics plus the multiplier and sinus generation) and on the right you can see the integrator capacitors and the adders.


The question now is what to do with one... well doing a "fall of object without drag" is quite interesting and easy, doing other ballistic experiments is also interesting... See the presentations at the Analog Computer Museum.


2017-01-05

Monster-B-Gone

Last year Make:Magazine had an article where they built a Monster-B-Gone detector. I did not had the same processor board (a trinket) and having a stash of Attiny15L, I thought I could use them instead.



There is one big problem with this MPU, speed. It only runs at 1.6MHz, meaning that the cycle time is 625ns. The Neopixel needs a feed of serial zeros and ones where minimum on-time is about half of that.
So I needed to get clever...
First I read a lot about Neopixels (here and here), then I decided to use the PWM generator to drive the Neopixels with the PLL, this would allow a faster impulse generation that the processor could do.
I had to compromise on the number of colors available (only 7) but in the end it worked. So that the 8 bits of a color byte always have the same value (there are 3 color bytes for each pixel). This not only is needed because of the speed, but also because the processor only has 32 byte registers.
The other components is a LiPo battery, a LiPo charger, a push button (resets the processor) and the neopixel (all from adafruit).


My Kids required one each... so ...


How it works required lot of cycle counting, but in the end I made it work! So first set up the PLL for a suitable upscaled frequency, then create the rolling blue light (walking one) and after some random rounds, show the green ring (room clean). There are lots of discussions if it should occasionally show the red light (MONSTER IN ROOM). I decided it should never show the red light, but changing the code to use the same random number generator to decide should be easy.

video
 The code is here.

2016-08-08

ATTinys

I finally have the time to post some old projects (some of witch I'm taking the opportunity to finish). These are all around the now dead Attiny15L from Atmel, but the techniques might be used in the newer tiny Atmel (Attiny25,45 and 85, Attiny10 Attiny104, etc). I write might because this first post probably will not be very useful for these newer devices, as the calibration of the internal oscillator has changed from the ATTiny15 times.
First I'll present my test board, many moons ago, the DIP Attiny15L was much more expensive than the wide SO8, so I built a board with the SO8 and the ISP connector with a 0.6 inch footprint. This way I could save space on the test board and use the cheap Attiny15 in SO8. I've recently uploaded the board to OSHPark so you can order it. You can also use the board for other SO8 Tinys (like the Attiny25,45,85 or tiny13). The board includes a Reset pull up resistor and a supply bypass capacitor (all optional if you know what you are doing).


This program just ouput a PWM sine wave (of 195Hz) on the OC1 output. The makefile takes care of programming flash, eeprom and the clock calibration on the last flash position.
I used an GNU octave script to generate a raw file of 64 bytes of a sampled sine wave.
The program just sets the calibration value, then sets up the Timer 1 for PWM at 12.5kHz and then goes on to read from the EEPROM the values in succession. The idea is to have a basis with the ATTiny to produce sound or voice.
On the bottom there is an Arduino board an a breadboard shield that I use to power the ATTiny and also to use as a serial to usb converter (the ATmega328 on the lower board has been removed).
There is a low pass RC filter on the output to get the 195Hz otherwise the PWM frequency appears. The blue box on the right is my AVRdragon.


One always thinks what will happen when pastebin is gone... and where all this code will end... no I don't... just kidding :-)

2016-06-12

An ARM experience

Well... we're back at writing.
Two years ago NXP lauched a 8pin dip ARM with 4K FLASH and 1K RAM, lots of people started doing things with it, as most other ARM processors (even Cortex M0) are multi-leaded-smd-monsters. This one, on the other side, looks like an ATTiny85 in its PDIP8.
This weekend decided to try it out. I just followed the herd, although not the common route. I followed this tutorial and bought this "starter kit".
I used one LED and the two switches that come in the bundle to wire one LED output as the example and one switch for the RESET and the other to force the bootloader.

I used two machines for the LPCXpresso installation (you do have to register to get a free non limiting license, but if you can't be bothered for this processor you don't need to). You will need to install some extra packages, follow the procedure in this link. I managed to have LPCXpresso running both in OpenSuse 13.2 and Leap 42. In Leap you need to install the 32bit packages instead of the x64. Download the LPC810 Codebase example from here, import the project and build all. No joke, it is that simple.
Since I'm running linux, the alternative loader is this one. Like most linux command line programs, it is crude and simple. Just download, extract and type make.
Just copy the example command line with the your hex program (it is in the Release directory in the workspace project folder).
and yes... it blinks!
The processor has lots of embedded resources but only 4k of code might be the limiting factor. Still it is very interesting, in particular if you can save more power than an ATTiny and when needed produce way more MIPS.
For a first post after such a long hiatus it was not bad... more to come :-)