The idea behind this board is: build general purpose Arduino but very much lightweight (similar to the bare bones). Skip the form factor, but make it possible to connect sensors and servo's directly. Make it possible to use in breadboard, but also as small standalone module. Make it flexible, yet as compact as possible. It is by no means meant as competitor to the standard Arduino boards, it is tailored for easy building (few parts, all trough-hole) and easy connection (lots of connection points, standard pin-headers, standard grid size).

This board was previously dubbed 'CheapDuino' but after a discussion with Tom Igoe this board has been renamed 'ottantotto' which is italian for eightyeight (since the board is using Atmega88 controllers)

In the following section the features, schematic, pcb and partlist. After that a section on tailoring your ottantotto built…

• PCB can be splitted into two parts: the MAX232 section for programming and communication and the microcontroller itself.
• ATmega88, 168 or 328
• ceramic resonator (three legs). Crystal can be mounted on backside of pcb.
• two general purpose LED's
• 100uF capacitor or 1000uF (small footprint) for use with RC servo's
• LM7805 (can be bypassed by wire or diode)
• MAX 232 (or equivalent)
• m3 mounting holes
• Db9 female connector (solder version)
• signal - VCC - GND servo style three-terminal connectors
• DTR line is used for reset. This allows the arduino environment to program the chip using a bootloader

Orcad PCB design files

The following files can be send to a pcb pooling service.

board size: 2900 mil x 1050 mil - 73.66 mm x 26.67 mm

ottantottogerber.zip (can be submitted to eurocircuits)

This PCB can be cut into two pieces, the microcontroller board and the programming dongle.

The design is made in a way that you can either use a PCB (double sided) or just build it on soldering-breadboard. I decided to build a true-to-scale ottantotto on breadboard. The backside is reasonably simple to solder.

The programming adapter is slightly larger than the PCB version, but the reset functionality using the DTR line works well.

Below an order list for farnell. Since the mega88 is not much cheaper there (get them from Ledsee), a mega168 will do even better (no changing of firmware). In the list cost effective numbers are chosen (to which bulk rates apply). A choice can be made between using an LM7805 regulator (so the board is 12V proof) or a simple diode (0,7 V drop → battery operation up to 6V works)

and pin headers:

(2 36pin headers are necessary to populate the whole board. The 5way socket is necessary when separating the MAX232 programmer dongle from the board)

The design is very flexible, so the board can be build in a number of 'flavours' tailored to your needs:

This is the board completely populated. It works similar to a serial arduino (except that the power connector is wired to the board) In this way the board can be used as stand-alone microcontroller system, or build in somewhere. The serial port is fully available.

When only the connectors at microcontroller-pin -side are connected, the board can be used as test module for solderless breadboard. the positioning of power connection (- and +) allows for breadboard connectivity too.

When the PCB has been cut, both of the boards can be populated independently. This allows for a very compact board (which can be used for controlling mobile robots such as the flatpack-walker (check http://www.retrointerfacing.com) or an 18-servo walker (softservo)

The programming dongle can be used separately

On the silkscreen of the PCB no room was left for the pin numbers. A simple solution is to print out the following image and to glue it on the microcontroller! ottantottopins.pdf The pin numbers are according to the Arduino standard: PD0 tm PD7 are numbered 0 to 7. PB0 tm PB5 are numbered 8 to 13. The analog pins are numbered a0 to a5 and represent PC0 to PC5.

Power can be connected in numerous ways, depending on the 'flavour' of your board. An adapter plug can be connected using wires, you can also connect a battery pack directly to any of the power pins. A linear regulator (7805) can be mounted in the reserved space (TO220, standing up). This chip is used when you solder the battery leads directly to the - and + connector next to this footprint. On the same footprint you can also mount a 1N400x series diode, as 0.7V drop / reverse polarity protection. (wired from pin 1 to 3, fold the legs tight). You can also wire the power directly to the rail (the pin-tracks on the outside and center side). Be sure not to connect power exceeding the 6V this way, since the avr won't stand it…

The board is Arduino compatible, so the arduino environment can be used to compile sketches and upload them to the board. The dongle part needs to be in place (when you built the 'compact' version) and a serial connection between the dongle and PC should be established. See this page on setting up the environment and programming the board.

I Recently discovered that the combination Mac OSX + PL2303 + driver does not work. Apparently the Auto-reset function using the RS232 DTR line does not function long enough for the bootloader to stay in contact. The board does reset, but after that immediately starts up its program.

Normally the Arduino environment uses both the RTS signal and the DTR to reset the board, so either one of them can be used. See arduino forum. However, with Mac OSX the RTS signal seems to work better. The Workaround is simple: convert the programming dongle or programmer part of the ottantotto to use the RTS instead of DTR signal.

First, disconnect DTR (pin 4 on the DSUB-9 connector) from MAX232 pin 8 by scratching the pcb track (see red circle):

Then make a connection between RTS (pin 7 on DSUB-9 connector) to MAX232 pin 8 by soldering a wire on the bottomside:

After this modification, the dongle should work with Mac OSX too.

The bootloader is adapted from the standard arduino bootloader for atmega168. Look here for a more elaborate page on bootloaders The sources can be found here With winavr installed (I did not use arduino to compile the bootloader, but it should be possible anyway), you type make atmega88 from a command prompt, and the correct version will compile. Point is that the atmega88 has the same memory footprint as the mega8, but the same internal configuration (registers, timers, uart, interrupts as the atmega 168)

a new entry to the boards.txt file has been made that resides in the 'hardware' directory. boards.txt (zipped)

##############################################################

atmega88.name=Ottantotto with ATmega88
atmega88.upload.protocol=stk500
atmega88.upload.maximum_size=7168
atmega88.upload.speed=19200

atmega88.bootloader.low_fuses=0xff
atmega88.bootloader.high_fuses=0xdd
atmega88.bootloader.extended_fuses=0x00
atmega88.bootloader.path=atmega168
atmega88.bootloader.file=ATmegaBOOT_168_atmega88.hex
atmega88.bootloader.unlock_bits=0x3F
atmega88.bootloader.lock_bits=0x0F

atmega88.build.mcu=atmega88
atmega88.build.f_cpu=16000000L
atmega88.build.core=arduino

Besides the board.txt file, also a number of sources need to be altered. Since the processor is mostly compatible with the atmega168, except memory sizes, the c-files in the hardware\cores\arduino directory needed to be altered. Every entry #if defined(AVR_ATmega168) has been replaced with #if defined(AVR_ATmega168) || (AVR_ATmega88)

here you can download the new directory hardware/cores/arduino hardware_cores_arduino.zip. This is the hardware cores directory for Arduino011 or even earlier and is far from complete. When compilation of libraries throws up warnings, the replacement strategy mentioned above normally suffices.

From version 0013 (according to GIPLT) no warnings are thrown, so only adding the ottantotto section described above suffices.

The standard Arduino Blink example with LED on pin 13 does not work, because… we have two LED's on pin 8 and pin 9 instead.

// The basic Arduino example for ottantotto  
// Turns the red and green LED on and off intermittendly
#define red 9
#define green 8
void setup()              // run once, when the sketch starts
{
  pinMode(green, OUTPUT); // sets the digital pin as output
  pinMode(red, OUTPUT);   // sets the digital pin as output
}
void loop()               // run over and over again
{
  digitalWrite(green,HIGH); // sets the LED on
  digitalWrite(red,LOW);
  delay(100);               // waits for 0.1 second   
  digitalWrite(green, LOW); // sets the LED off
  digitalWrite(red,HIGH);
  delay(100);               // waits for 0.1 second
}

1. Why not add the ftdi232? Because SMD soldering makes it more difficult for inexperienced people to solder the board. The FTDI chip is also 8 times the price of a MAX232 clone. You can buy ftdi-style USB-2-serial cables for EUR 6,-
2. why all the extra ground and vcc pins? For every servo or sensor you connect to your arduino, you need supply voltage and ground. Normally on an arduino you would use a protoshield, a breadboard, or a mess of interconnected extra wires.
3. Why splitting To make it even smaller!
4. where can I get one? The first batch of 50 has arrived and is ready for testing. The versions I tried out seem to be working fine. Price for a bare PCB is EUR 2,- (ex. vat and p&p) Since I'm not intending to become a web shop, I'll ship a couple while the stock lasts, in exchange for posting your experiences etc. here on the wiki. In addition to the boards I ordered some stock in ATmega88's, so I can ship them too if required. Please contact me by email in case you're interested.
5. the docs for the generic max232n's say to use 1UF caps and not the 10UF caps you have in your parts list. Is this just extra protection? All the pegel converters i've built are with the generic max232n with 1UF caps or the max232cpe with .1UF caps. Only the - very - old max232 drivers need the full 10uF cap storage for boosting the signals, all modern equivalents do it with less (1 uF) - even some with 100 nF. I chose to play safe and use 10uF caps, so they all work. No problem to use a max232n and use 1uF caps instead of 10uF.
6. where does the 7805 voltage regulator fit on the circuit? It is on the programming dongle part right? I was concerned that maybe you have the 7805 in one of those tiny packages not the big normal 7805's. Regarding the 7805, on the top-side of the chip (near pin 1 and 28) is a 3-way space left to place it, heatsink towards the chip. You can also chose NOT to place it, and have a diode instead (from pin 1 to 3 of the same socket). This component (either 7805 or diode) is only used if you place the power connection on the separate + and - wires next to it (if this is unclear, I can mark the spots in a picture). If you plug in a battery directly to the power rails (as shown in the pictures of the 'minimal' version) then neither the diode or LM7805 is used or necessary. Atmel's can take up to 6V, so with 4 NiMH batteries you're safe enough to power the board directly from 4 batteries. I'd personally recommend using the diode, since it is an extra safety measure against swapping power wires, and it takes of 0.7V excess voltage.
7. can you flash the bootloader onto the microcontrollers directly with the programming dongle or do you need a chip programmer on top of that for the first bootloader flashing? Yes, you need to flash it on beforehand. You'll need a normal atmel programmer (or send the chips to me, and let me do it) I use a dragon with ZIF socket. See the page on bootloaders. You can make an ISP adapter cable for connecting it to an AVR-ISP MK11 (USB) or MK1 (serial) programmer, or any parallel port ISP adapter that you have lying around. I made a cable which plugs on the ottantotto board using two 3-pin connectors: one at the reset (pin 1) + VCC and GND, and another 3-pin header with MOSI, MISO and SCK connecting to the three pins for that (pin B3,4,5). Don't forget to set the correct fuse bits too: make the chip run on external clock, disable the clk-DIV-8 bit, enable the bootloader reset (see normal arduino settings) (hex settings of fuse are 0xFF 0xDD on top of my head)→ if this is unclear to you, let me know, than I will elaborate a little on it on the wiki.
8. on the schematics, c1 is listed as 100uF, and in the parts list you have a part that is 1000uF. mistake or old version? 100uF is normally ok. When using RC servo's, such as with the tinywalker, 1000uF is necessary, that's the confusion.
9. also, the resonator is a very hard part to source in the us. any suggestions? Regarding the resonator, you'll need one with three legs, built in capacitor. You could also opt for a normal crystal and two capactitors (which would have to be mounted on the bottomside of the pcb..) so the three legged resonator is most price efficient. You listed a suitable one as far as I can see. (I cannot reach newark, but farnell lists your part as US supply - farnell ) alternatives are digikey, digikey #2 or mouser

During toko#14 a number of wishes for the next version has been formulated.

• make two versions: one with FTDI and USB connector (using the same separation) and one serial. Add LED's?
• Revise the serial port part: check polarity of capacitors, and add a supply capacitor
• make it possible to connect the power rail pre- or post regulator (see softservo)
• put the power-section of the board to the other side: add a power connector (board will be larger) - still with possible cut
• remove groundplane round mounting holes
• put LED on same pin as arduino

In this section version 2 of the ottantotto board is presented.

Today a first batch of 100 has been ordered! — edwin dertien 2010/06/29 16:45

The exact sizes are 90.68 mm x 26.67

• Power section has moved to other side, board is longer!
• total size has increased by 1.5 cm in length. (power section). The rest remains exactly the same.
• hole diameter has not changed! This diameter is not exactly 3 mm, so for example 3mm plastic studs clamp in nicely.
• cutting spaces are bigger (+0.5mm)
• both power section and serial section can be cut.

• all 100nF capacitors has been changed to 100mill grid space instead of 200mill
• all resistors have to be mounted straight up (not flat)

• Power section contains socket for standard adapter plugs, protection diode and power LED
• The power rail can be connected with a jumper to the Vin or to the 5V (VCC)

• The 1000uF cap has not changed. Since normally a perfectly ordinary fitting 100uF cap can be used, the spacing problems only occur when using the big 1000uF on that space.
• RESET connection is no longer in the pin-row, it is on the ISP header, In its place is the power rail selection jumper

Carefull with this jumper: it is meant to connect RC-servo's directly to the battery source, after the voltage regulator. The default position is to the 5V!

• Serial section has been extended with TxD and RxD LED's so upload can be monitored as well as standard data transfer
• an extra 1uF cap is added to the RS232 section (official decoupling)
• the V- capacitor has been rotated (non-fatal-error in previous design, most max232's are redundant) but neater…

• One LED has been sacrificed. The remaining LED has been attached to PORTB.5 where on normal arduino's also the LED is located

• The 6-pin ISP header has been added
• the reset function on the ISP header has a jumper too. This can be used when the ISP header is used for the sdadapter, so a different line can be chosen for the MMC-CS

All three versions: full, breadboard and compact are still possible. The breadboard version is different from the original

• breadboard version is still possible: use the VCC from the analog jumper, and a separate ground pin for power-to-breadboard

See schematic below:

or as pdf: ottantotto2.pdf

An overview of the PCB: pdf's of the print layers: ottanbottom.pdf ottantop.pdf