ArdoMite and ArdoMite S

This is a PicoMite in the general form factor of the Arduino UNO.
There are two different versions with different sets of Gerber files:

ArdoMite
This is in the same form factor as the UNO. All connectors and fixing holes are designed to line up with those of an Arduino UNO. As such it can often be used as a mechanical drop-in replacement. Arduino shields can often plug into it but the Arduino system depends heavily on libraries for many shields and these are not available to the PicoMite so you are on your own when it comes to getting anything to work.

ArdoMite_S
This is identical to the ArdoMite electronically and has the same circuit, but the mechanical side of things is different. The main difference is that, unlike the Arduino UNO and ArdoMite, it is breadboard-friendly. All connections and fixing holes are on a 0.1" grid. This makes it easier to work with in many cases and it may, from some suppliers, be cheaper to produce the PCBs as there is less work involved in shaping them. Of course, with the connectore rearranged, the S version is NOT compatible with Arduino shields. It does allow DIY shields made from pad or strip board to be used though.


Both models share the same pin correlation with the UNO:

Arduino             ArdoMite
UNO R3

1  Blank            /TP5              Transistor collector
2  IOREF (3.3 or 5) 3V3               Input voltages shouldn't exceed this.
3  PC6 - Reset      RUN
4  +3V3             3V3
5  +5V              5V
6  GND              GND
7  GND              GND
8  VIN              VIN

9  PC0 - A0         GP26/ADC0
10 PC1 - A1         GP27/ADC1
11 PC2 - A2         GP28/ADC2
12 PC3 - A3         GP13              No A3 on PicoMite
13 PC4 - A4         GP14/I2C2_SDA     No A4 on PicoMite
14 PC5 - A5         GP15/I2C2_SCL     No A5 on PicoMite

15 PD0 - RX         GP17/COM1_RX
16 PD1 - TX         GP16/COM1_TX
17 PD2 - INT0       GP12
18 PD3 - INT1/PWM   GP11/PWM5B
19 PD4              GP10
20 PD5 - PWM        GP9/PWM4B
21 PD6 - PWM        GP8/PWM4A
22 PD7              GP7

23 PB0    GP6
24 PB1 - PWM        GP5/PWM3A
25 PB2 - SS/PWM     GP21/PWM2B
26 PB3 - MOSI/PWM   GP19/PWM1B/SPI_TX
27 PB4 - MISO       GP20/SPI_RX
28 PB5 - SCK        GP18/SPI_CLK
29 GND              GND
30 AREF             VREF            Not identical in function.
31 PC4 - SDA        GP0/I2C2_SDA
32 PC5 - SCL        GP1/I2C2_SCL

A3. A4 and A5 are not available.
All I/O is at 3V3, not 5V.

-----------------------

ICSP Connector
1 MISO2             GP28/SP2_RX     Also ADC2
2 5V                3V3             Not the same as Arduino
3 SCK2              GP26/SP2_CLK    Also ADC0
4 MOSI2             GP27/SP2_TX     Also ADC1
5 RESET2            RUN
6 GND               GND


There are some major difffereces to the Arduino:
? Most obvious - the ArdoMite is based around the PicoMite, a Raspberry Pi Pico running the MMBasic interpreter by Geoff Graham and Peter Mather. :) 
> The ArdoMite has no 5V tolerant pins. The voltage MUST NOT exceed 3.6V on any pin.Any pin that would normally source 5V (with the exception of the 5V pin) will only source 3V3.
> The available source/sink current on any single pin is 12mA, but the voltage will sag to approximately 2.3V. A more useful limit is 5mA, at which the output voltage is maintained to approximately 3V..
> The maximum total source/sink current for all the pins combined is 50mA. This is the limit for the RP2040 chip.
> Interrupts are handled at the end of each MMBasic line. There are no direct hardware interrupts like INT0 and INT1. However, all pins can be interrupts. 
> The ArdoMite and ArdoMite S only have three Analogue inputs. Unfortunately, due to a bug in the RP2040 chip, these can only be regarded as accurate to 8-bits.
> The ICSP connector is not for programming! It merely gives access to SPI2 for those shields that require it. Note that these are also connected to the ADC pins so SPI2 and the analogue inputs are not available at the same time.
> Reset and Reset2 do the same thing, a hardware reset by pulling down the RUN pin on the PicoMite.
> All programming access is by using a terminal program such as Tera Term on a PC connected via USB. This can also be the power source while programming.
> Other PWM pins can be specified in addition to those listed.
> AREF works slightly differently. The reference input is normally connected to 3V3 via a 200R resistor. You can connect a LM4040 3V device between AREF and GND to reduce the reference voltage to 3V. This gives improved operation of the ADC inputs. Setting OPTION VCC 3 will then scale the pin() values correctly. The UNO allows for injection of an external reference voltage rather than this system.


The /TP5 pin (not used on the UNO) is the inverse of the green LRD on the PicoMite. When the LED is on the /TP5 output is pulled low. It is an open collector output that should be able to handle at least 60mA. Note that if you use it to drive a relay then you MUST fit a back EMF suppression diode across the coil. By default the LED acts as a "heartbeat" and will flash continually while the power is on. Your program can defeat this by using the command OPTION HEARTBEAT OFF. It can be reinstated with OPTION HEARTBEAT ON. While the heartbeat function is off you can use:
SETPIN GP25 DOUT  'to use it as a digital output
pin(GP25) = 1  'to turn the LED on and make /TP5 low
pin(GP25) = 0  'to turn the LED off and make /TP5 open circuit
The specified BC337 transistor can switch up to 40V.and about 600mW.


Components:
Just a couple of points.
> The micro SD card holder is optional, but if you use it you will have to get the correct model for the solder pads to line up. It appears to be reasonably easy to get from the larger suppliers. I would suggest fitting this component first to reduce the chance of heat damage to the PicoMite.
> Most standard barrel jack sockets will probably fit, Some will project further from the edge of the PCB than others. The iten shown is 14.5mm long.
> Tiny holes (0.45mm) have been made in opposite pads for the PicoMite. These can be used to get good alignment.
> The holes for the I/O pins are intended for female headers. They will probably be too small for most male headers.
