Two 10K resistors (R10,R11 above) divide the input voltage in half, making it possible to measure up to 6.6volts with the 3.3volt PIC microcontroller. Has your project ever mysteriously stopped responding because of an accidental short circuit? The Bus Pirate’s power supplies are equipped with voltage monitoring that can detect a change in power levels.Įach monitored signal is connected to an analog to digital converter (ADC) through a resistor voltage divider. Voltage monitoring is a new feature we’re really excited about. In practice, and under light loads, we see less than 0.1volts drop-out from VR4. VR4 (5volts) will lose about 0.2volts, but 4.8volts remains well within the acceptable range for most 5volt chips. VR3 (3.3volts) has plenty of headroom to operate from a 5volt supply. VR2 will work well above 10volts, and provides an adequate supply for the other regulators. We did this because the maximum input for VR3 and VR4 is 6volts, leaving the device with a narrow 5.2-6volt power supply range. The switchable regulators are powered by VR2, a 5volt supply. An additional, optional, 0.1uF capacitor (C12,C11) can improve regulation. The datasheet specifies a hefty capacitor on the input (C23, C21) and output (C24, C22) pins, we used the same 10uF tantalum we use everywhere. A pull-down resistor (R13,R12) ensures that the regulators are off when the PIC isn’t actively driving the line, such as during power-up initialization. A high level on pin 1 enables the regulator. VR3 (3.3volts) and VR4 (5volts) are TI TPS796XX voltage regulators with an enable switch. We got so tired of this routine that we added a software controlled reset to the updated design. If a misconfigured IC needed to be power-cycled, we had to disconnect a wire. A major annoyance was the lack of a power reset for connected chips. The original Bus Pirate had dual power supplies, 3.3volts and 5volts, so most ICs could be interfaced without an additional power supply. 7-10volts DC is probably the ideal power supply range. J1 is a power supply jack for a common 2.1mm DC barrel plug. Both require two 0.1uF bypass capacitors (C3-C6). VR1 is a 3.3volt supply for the microcontroller and RS232 transceiver. If you have any ideas, please share them in the comments. We couldn’t find an elegant way to control an arbitrary voltage pull-up resistor array from a 3.3volt microcontroller. Through-hole resistors are used like jumper-wires to make the PCB easier to etch at home. The updated design has pull-up resistors (R20-23) on the three main bus signals (data in, data out, clock) and the chip select (CS) pin.Ī row of jumpers (SV5) connects each resistor to an external voltage supplied through the Vext terminal (X4). The original Bus Pirate has 3.3volt pull-up resistors on 2 pins, but most of our tests required additional external resistors. The serial interface will work with a USB->serial adapter. This chip replaces the expensive through-hole MAX3223EEPP+ used in the previous version of the Bus Pirate. Read more about this chip in our PIC24F introduction.Īn inexpensive MAX3232CSE RS232 transceiver (IC2) interfaces the PIC to a PC serial port. A 2K pull-up resistor (R1) is required for the MCLR function on pin 1. The chip is programmed through a five pin header (ICSP). The 2.5volt internal regulator requires a 10uF tantalum capacitor (C20). The power pins have 0.1uF bypass capacitors to ground (C1,2). We used a Microchip PIC24FJ64GA002 28pin SOIC microcontroller (IC1) in this project. All the files for this project are included in the project archive linked at the end of the article. The circuit and PCB are designed using the freeware version of Cadsoft Eagle. Voltage monitoring of all power suppliesĬlick for a full size schematic image (PNG).Software resettable 3.3volt and 5volt power supplies.Pull-up resistors on all bus lines with external voltage source.This article introduces an updated design with new features and a bunch of improvements. We released it in a how-to and used it to demonstrate a bunch of serial interface ICs in our parts posts. The Bus Pirate started as a collection of code fragments we used to test new chips without endless compile-program-run development cycles. We cover the design updates and interface a digital to analog converter below. Check out the new Hack a Day Bus Pirate page, and browse the Bus Pirate source code in our Google code SVN repository. There’s also a firmware update for both Bus Pirate hardware versions, with bug fixes, and a PC AT keyboard decoder. Based on your feedback, and our experience using the original Bus Pirate to demonstrate various parts, we updated the design with new features and cheaper components. We use the Bus Pirate to interface a new chip without writing code or designing a PCB.
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