INTERFACE FIRMWARE - DX air curtains project

INTRODUCTION The purpose of this document is to define the firmware requirements for a new PCB development of a Control Interface for HVAC unit. ELECTRIC CONTROL INTERFACE: Designed to control the two-speed fan motor and the electric heater for temperature regulation (two stages). BASIC OPERATION: At start-up, frequency must be tested during 2 seconds using ZCD signal. No operation is allowed till reach an stable frequency inside valid range 40Hz to 70Hz. Switch ON AC power RELAY when all is ok. At this moment the interface waits for MODBUS-RTU commands. Fan speed control: low / fast / stop (2 digital lines). Very important: changes in speed must be synchronized with ZCD input signal. It’s very important to give the maximum priority to any modbus command from master. 20ms is the maximum allowed delay to execute the order. ZCD signal control, corresponding to AC line frequency. Alarm if it’s out of normal range (40 to 70 Hz), or is unstable. This signal must be measured every semi cycle using a uC timer: if it’s <5ms or >20ms then FAN must stop and RELAY must be switched off. 2 input digital signals & 1 output signal for users application. 1 PTC1000 temperature sensor for users application, read using internal A/D converter of microprocessor. To avoid noise, read minimum 64 samples and get a mean value. Led Indicator Status/Alarm: fast blink during communication and slow blink for alarm codes. 3 output digital signals for control 3-stage heater Proposal phases / milestones of firmware project: Electric control interface Basic operation (including MODBUS) Heater Control & Advanced functions for safety