Powering the HW Environment
The hardware environment is an essential part of deploying your project. Initially, you will most likely test your code on a development board, and then deploy the tested code to the target PCB.
The PIC Microcontroller requires a low DC voltage supply, in a range from 1.8 Vdc to 5.5 Vdc. They are voltage supply sensitive and do not handle over-voltage supplied to the device.
The polarity of the supply should never be reversed, as this damages the PIC. Depending on how long the device is subject to a reversed supply will depend on the eventual damage, with the eventual outcome being an unusable device.
The easiest way to determine which voltage level is required would be to consult the datasheet for your device. Some tips or general rules are below.
- An F device or PICxxFxxx can be powered between 1.8Vdc to 5.5Vdc
- A K* device or PICxxFxxKxx can be powered at 3.3Vdc and 5.5 Vdc
- A J** device can only be supplied with a voltage level from 1.8Vdc to 5.5Vdc
- A J device may have 5.5 VDC tolerant inputs
- An LF device or PICxxLFxxx, is a low-frequency device available across the range.
*Some K devices are limited to a 3v3 supply voltage.
**The voltage level at which the PIC is powered generally determines the voltage at which the inputs can be triggered. Where that voltage input level is limited. ie the J types, using a voltage supply higher than the J's supply voltage will damage the device.
The RADIX development boards have two voltage levels to consider,
- The input supply
- The PCB's operational voltage
The input supply is what is delivered to the board before it is regulated down to a usable level. The voltage must be DC and can range from 8 Vdc to ~ 24 Vdc. Once the board is powered, the operational voltage can be selected.
In most cases, a RADIX development board has an LDO or Low Dropout Regulator installed on the PCB. This means that only a nominally higher voltage is needed as the LDO regulates the voltage efficiently. When you apply a very high voltage to the PCB, this will cause the LDO to heat up, and it can cause premature failure of the device.
The operational voltage will be either 3v3 or 5Vdc, and the regulator on the PCB outputs this voltage. Selecting the voltage is done by either moving the jumper to the correct position or moving a DIP switch to the correct position.
Changes to the operational voltage should only be done when the PCB is powered down. Moving the jumper or moving the DIP switch selection can cause the regulator to stop regulating and voltage-sensitive devices on the PCB for a short time will be exposed to the full input voltage.
The USB connector found on the RADIX development PCBs is tied into the power circuit and the PCB is protected using a ferrite bead. Since the USB port can supply up to 500mAmps, you can to a limited extent power the development PCB from your laptop or desktop PC's USB Ports.
The USB power is isolated from the development board using a jumper or DIP switch setting depending on the RADIX model.
The quality and consistency of your supply to the PCB is important for the success of your project especially when deployed.
