The power supply for the PIC Development PCB plays an important role. Not only must the DC be delivered at the same consistent rate, but it must also be stable. Fluctuations in the power supply affects the PIC and can result in unreliable and unpredictable results. One result can be that PIC stops stepping through the code, similar to an airplane stalling. The only way to recover from such an event would be to manually of physically restart the PIC.
One problem which can result is referred to as Brown Out : Reduction in the voltage or supplied power. It is caused either by the failure of generation, transmission, or distribution system, or inadvertently when demand exceeds supply.
This problem can be managed by using a watchdog timer. This timer resets the device, if it itself is not reset after a period of time. The watchdog timer is a useful tool for critical applications that cannot be interrupted or who need to recover from unexpected events.
The above problem can result from an AC / Mains blackout, transient or power surge or if the case of a battery powered system, the battery runs low and is no longer able to maintain the power requirements of the PIC application.
In more mainstream applications, a UPS of some sort is connected in line with the power supply as a backup and provides the necessary time or leeway until power can be restored.
For the hobbyist however, just getting 3 or 5 volts to your PCB is the biggest hurdle and can be achieved quite simply.
Shown left is the simplest, cheapest and easily available power supplies which can be used for hobbyist applications. There are a number of attachments which enable the power supply to be adapted to almost any and all available connector types.
As can be seen on the front of the power supply, both the polarity and the voltage level can be set.
This is useful for when assert the correct DC power required for the PCB to run.
All PCBs shipped by ZarDynamix, include a voltage regulator, which on its output delivers the required voltage. This means that the input voltage must be higher by at least 30%. There are two types of voltage regulator, your standard linear type and a LDO (Low Drop-out Regulator). The LDO types are featuring more regularly in our designs as it means that the input power required is lower, and battery packs are possible, which is the more practical option.
Once connected to the ProtoDev, the voltage regulator or regulators regulate the voltage down to the required operational level. PICs are sensitive and exceeded the input voltage can simply damage the PIC beyond use.
The Protodev DX and ProtoDev 20 have multiple selection via jumpers to select which power level to supply to the PIC. In both cases, the PICs supplied with these PCBs use 5dc. Although, by changing the jumper selection, the PCB can run at a lower voltage.
PICs are available in a number of types, namely LF, J and K which are specifically designed to cater for lower voltage operations, especially if you need to maintain or require a specific operating frequency.
The operating frequency can be set by the device in terms of the limited operating range, which means for example a PIC 16F887’s maximum operating frequency is 20 MHZ or 5 MIPS.
In the next article, we will look in a bit more depth into the on board power supplies which the PIC uses and how to configure them.