we are from peas technologies, we are doing embedded and software development, recently i did similar project for RaspberryPI, we are using IO card with 24 digital input, 16 relay outputs, 4 PWM outputs, high speed 2 counters, 10 low speed counters, timers etc.,
i read your requirements, and wish to list following features in your development,
our development include PCB design, full source firmware and software (as sdk)
1. 8-Digital Isolated Inputs
2. 2-High Speed Counter Inputs
3. 8 Channel 10 bit Analog input
4. Onewire Communication
5. I2C/SPI
6. 1-RS232
7. 2-RS485
8. 8 Relay Outputs
9. 2 - DAC
10. 2-PWM/4 Channel Bridge PWM