Voltage dividers for 5volt Arduino and 3.3volt SPI devices

I am setting up a radio module to plug into an Arduino.
Specifically the RFM12B like in this schematic;
http://www.flickr.com/photos/jeelabs/3297526692/in/photostream/#/

The Arduino runs at 5volts and the RFM12B runs at 3.3volts. So I have to convert the line levels from 5v -> 3.3v on the inputs to the SPI device and from 3.3v -> 5v for the output.

The example has a 4K ohms and a 10K ohms resistor for the 5v to 3.3v voltage dividers for the Arduino output data lines into the RFM12B, does that sound reasonable?


I did the math and worked through the examples on the Arduino tutorial site and came up with the following values; 1.5K ohms, 2.2K ohms

72, Kim

Arduinos in from Little Bird Electronics today

Last Sunday I ordered a few components from Little Bird Electronics.

A Arduino Duemilanove, several bare Arduino Atmel328, 74HC595, DIP sockets and a bunch of sparkfun stickers. The RTFM stickers are popular ;)

So, some of these bare Arduinos will be used for the lantern prototypes. Some for mcpu for the Nintendo controllers with the ISM band wireless stuff I got last time, one for a controller for a VFO/DDS for my receiver projects and some for temperature logging with a DS18B20. I got one full Duemilanove board to do the initial prototyping on and to program the rest. Should be fun =)

72,

Kim VK5FNET

How about a DDS tuned from an Arduino?

I received my Arduino back in 2009 at LCA. I've tinkered with it a bit and really haven't had to many bright ideas about what to use it for. I've been cutting some code recently for the magic lantern project, but the short version is, I need to place another order to get Atmel328s because the Atmel168s ran out of stock.

Anyhow, in the last order I to Little Bird Electronics I got some DS1077 programmable oscillators. They are a tiny little 8 pin SOIC. Been reading up about how to use them now. They have a I2C bus and there is a library for Arduino to bitbang out the commands to send out over I2C. Benlemasurier's DS1077 Library looks like it should do the job nicely. Now to find a carrier board to solder them up to, or perhaps make one...

What will I use them for? Well, a general coverage receiver is the obvious project. I think that that will be a while off yet, but its on the cards.

Kim VK5FNET

stage one prototype working

well the first prototype for the magic lantern has blinken licthen =) am pretty happy with how it turned out. it has six banks of three LEDs spaced evenly around the gap between the external ground rail and the internal power rail...

the arduino will sit in the middle of the inner ring, and all the transistors will be driven from the PWM pins.the leds will draw about 200mA when on full, need to figure out how much current the arduino draws. still need to work out a simple charging method. four AA cells should last several hours. this means that we can charge them from the solar panels directly with a suitable regulator. or we can pull the AA cells out and charge them from a 240v system powered by solar.

so, this is the first part of the magic lantern. todays work was all about displaying patters of light. the second part is interacting with other lanterns. this will require an RF module. however i haven't made up my mind about which module to use yet. it looks like the lobethal lights festival is already using a zigbee for another project, but these puppies start around $40 each. little bird electronics has a $9 module that might work quite well, but we would like to interact with other projects. more on the that later...

Photos here.

dreams of arduinos

Its one of those local public holidays today. Cup day or something. The kind that make you sleep in, warm enough to organise firewood and mow the back lawn. Well whats left of the lawn from the water bans and hot summer, but then theres the go inside time. Cool down with a chilled beverage and surf the 'net time.

I've been following the SolderSmoke blog and podcast, Bill mentioned that he put in a submission to Hack A Day about QRSS. Hack A Day is one of those sites that just gets the juices in the brain a pumping and thinking about building various things.

The first thing I found this morning was pluggable modules on an arduino shield, like lego blocks to enable fast prototyping of hardware and software.

The second was a two servo, four legged robot powered by four AA batteries and an Arduino.

The third was a tiny parallel supercomputer; the non-von1-supercomputer. There was another project a while back implementing a basic stamp supercomputer.

From a link somewhere I found one of the things that I keep crossing paths with, a home made Arduino board project. I found one today that set my mind racing off down the path of pluggable modules; the cheapduino.

So while not specifically parallel, but pluggable architectures of embedded systems. It could simplify the design of the individual board if a backplane had all the power, clock and a MPI interface for each CPU.

Perhaps a single USB connected backplane with a serial interface for each pluggable daughter board, in a simple frame that lets each daughter board have an edge connected I/O space. Something like the cards in a QBUS VAX. Smaller obviously, about five centimeters or two inches a side.

On that you could build a service per CPU, say, temperature logging, writing to a SD card, inrfa red comms., two wheeled robot platform built with servos, xigbee Tx/Rx, bluetooth...

I'm sure that there are loads of other ideas in this space. Its all about context and filling a need, its just strange some days where ones mind wanders... parallel pluggable embedded systems, which I'm sure one call call a mini-frame. Hmmmm ... theres an LCA talk in that I'm sure.


Kim VK5FNET