Nuts & Volts - May 2007

■ FIGURE 5. Microchip’s DM164120-1 development board.

■ FIGURE 4. A configuration for driving high-voltage devices.

Cmax = 42/[120 * ln ( 2.1/5.0)] Cmax = 0.4 µF

back of the motor. This may be a great way to make a serially controlled motor — similar to a serially controlled LCD module. (That also may be the focus of a future article.)

What I like most about these parts is the ability to run them off the same voltage source as the outputs you may be trying to drive. For example, back in the November ‘06 column, I showed some hardware interfaces to the PIC MCU. One of them showed how to drive some high-voltage devices using a bipolar transistor, as shown in Figure 4.

I don’t specify a voltage here, but instead just state B+. What if that was 12 volts, instead? Using the resistor and capacitor values I calculated above, I could control one of these outputs while also powering the HV PIC MCU from the same supply. Now, this will require some better filtering to prevent the large

voltage line from dipping quickly when the load kicks in, possibly resetting the PIC MCU. But, that may be easily solved if the load is fairly clean. This does offer a simpler solution than trying to add a separate voltage regulator.

Therefore, I chose a value of 0.1 µF — since it’s greater than 0.047 µF and less than 0.4 µF. We now have our PIC MCU regulator ready to go. One thing to note with this type of setup is the amount of current a shunt regulator draws without anything happening. The shunt regulator will draw 4 mA, even if the PIC MCU is in sleep mode and nothing else is connected. This is not an ideal setup for battery-operated devices that need long life. For those devices, you could use the PIC16F616 version of this same part, with an external low quiescent current draw regulator.

The HV parts are really handy, though, for applications that need a small component count. I’ve seen motors with the HV part built into the

DEVELOPMENT SUPPORT

As I mentioned, Microchip’s PICkit 2 programmer supports these parts. So does the latest version of my PICBasic Pro compiler — except for the PIC12HV615, which has just recently been released to the public. This is the eight-pin version of the PIC16HV616, so it’s got its own set of great applications. Can you imagine that part in a small surface-mount SOIC package without the need for a regulator?

I can already think of several applications where that could be squeezed into a tight sensor package. It could use an A/D port to read the sensor element and then send the value back via a one-wire serial connection. This

Order online at: www.melabs.com

Development Tools for PIC^® MCUs microEngineering Labs, Inc.

Phone: (719) 520-5323 Fax: (719) 520-1867 Box 60039 Colorado Springs, CO 80960

USB Programmer for PIC^® MCUs

RoHS Compliant

$119.95

( with accessories)

Programs PIC MCUs including low-voltage ( 3.3V) devices

Includes:
Programmer, USB Cable,
ZIF Programming Adapter for 8 to 40-pin DIP,
Software for Windows 98/Me/NT/2K/XP

EPIC^™ Parallel Port Programmer starting at $59.95

LAB-X Experimenter Boards

Pre-Assembled Board Available for 8, 14, 18, 28, and 40-pin PIC^® MCUs 2-line, 20-char LCD Module 9-pin Serial Port

Sample Programs Full Schematic Diagram

Pricing from $69.95 to $349.95

PICPROTO^™ Prototyping Boards Double-Sided with Plate-Thru Holes Circuitry for Power Supply and Clock Large Prototype Area

Boards Available for Most PIC^® MCUs Documentation and Schematic

Pricing from $8.95 to $19.95

BASIC Compilers for PICmicro^®Easy-To-Use BASIC Commands Windows 9x/Me/2K/XP Interface PICBASIC^™ Compiler $99.95 BASIC Stamp 1 Compatible Supports most 14-bit Core PICs Built-In Serial Comm Commands

PICBASIC PRO^™ Compiler $249.95 Supports All PICmicro^® MCU Families Direct Access to Internal Registers Supports In-Line Assembly Language Interrupts in PICBASIC and Assembly Built-In USB, I2C, RS-232 and More Source Level Debugging