Purpose

This document is intended to document the curve tracer This document will be updated through revisions and can be used as a persistent reference, regardless of the 'date posted'. As more information becomes available, documentation will be added.

The original post for the curve tracer can be found here. Note that the specifications have changed somewhat since project inception based on hardware limitations and other factors.

Current Revision

The current revision for the Curve Tracer is 1.2. The schematic and layout may have minor revisions released independently, depending on the scope of the change.

Document Current Revision Location
Curve Tracer Assembly 1.2 github
Schematic/BOM 1.2 github
Layout 1.2 github
Firmware -unreleased- github
Desktop GUI -unreleased- github

A "working" revision of all of the above may be found in the github repository.

Hardware

Curve Tracer, Top

Connection Description
P1 Header, 0.1", utilize for flash programming the microcontroller using a Microchip ICD3 or similar.
P2 USB Micro-B Connector utilized to create a Virtual COM Port for PC connection.
P3 XY header connection for probe tip terminals of an oscilloscope probe.
P4 Socket, 0.1", utilize to place a TO-220 or other through-hole components to be traced.
P8, P9 Pads for easy connection to the GND terminals of an oscilloscope probe.

Curve Tracer, Bottom

Connection Description
P6 Safety (multimeter) probe connector, 'positive'.
P7 Safety (multimeter) probe connector, 'positive'.

Connector Details

Each multiple-contact connector is detailed in this section. Connectors with a single function - such as USB - are not detailed.

ICSP - P1

Pin Description
1 ~MCLR/Vpp
2 +5V
3 GND
4 PGD
5 PGC

Probe Connections - P6, P7

Pin Description
P6 V+, positive probe connection.
V- V-, negative probe connection.

MOSFET/Transistor Connection, P4

Pin Description
1 A high-impedance voltage output intended to apply a voltage to a MOSFET or similar high-impedance device, also called the 'gate'
2 Positive probe connection, 'drain'
3 Negative probe connection, 'source'
4 'drain'
5 'source'
6 'gate'

Pin Specifications

Parameter Value
Maximum Absolute Voltage, V+, V- 5.0V
Minimum Absolute Voltage, V+, V- 0.0V
Maximum Differential Voltage, V+, V- 5.0V
Minimum Differential Voltage, V+, V- -5.0V
Maximum Current, V+, V- +/-20mA
Maximum Absolute Voltage, Vgate 5.0V
Minimum Absolute Voltage, Vgate 0.0V
Maximum Current, Vgate 2.5mA
Output Impedance, Vgate 2kΩ

Firmware

In order to compile and load the firmware yourself, you will need MPLAB X and the XC16 Compiler installed on your machine.

  1. Create a new project in MPLAB X (File -> New Project)
  2. Select 'standalone project'
  3. Select the device - PIC24FV16KM202
  4. Select the directory in which you would prefer to save your project
  5. Select the XC16 compiler, then the debugging tool that you will be using for programming (probably an ICD3 or PICkit)
  6. Add all *.h files into the 'headers'.
  7. Add all *.c and *.s files into the 'source'
  8. Enter the compiler configuration and select optimization -O1 or the compiler may not be able to allocate enough program memory. I usually like to isolate each function into its own section and tell the linker to remove unused sections in order to reduce memory usage.
  9. Program your board!

You will also need to change the configuration of the FT230X. Detailed instructions may be found on the blog.

User Notes

When this equipment is utilized as a curve tracer, it MUST be utilized without power applied to the unit under test (UUT). There are many varieties that emulate power off by going into a standby state, but this is NOT power off! Be sure that the device is completely unplugged and leave unplugged for several seconds to give any capacitors time to discharge.

Vgate is intended to hold a constant DC voltage across the gate of a MOSFET. Any resistive load placed on Vgate will potentially load Vgate beyond its driving capacity.



© by Jason R. Jones 2016
My thanks to the Pelican and Python Communities.