This DIY Curve Tracer Can Take a Variety of Component Measurements
Paul Versteeg's custom-designed curve tracer instrument has similar performance to its much more expensive counterparts.
What is a curve tracer?
When it comes to testing various aspects of electronic components, curve tracers are often the go-to device but can be rather expensive due to their complex and precise nature. They work by sending a predetermined mix of voltage and current across a component's terminals and measuring the resulting current levels. Based on these readings, aspects regarding the efficiency of tolerances of the device being measured can be seen on a two-axis graph, thus giving the tool the name "curve tracer." Paul Versteeg was interested in building a new one for himself from the ground-up to replace the curve tracer he already had, except this time, it would have nearly identical capabilities to off-the-shelf units while also being cheaper.
The specifications
Versteeg planned for a set of three primary ranges: 0-35V @ 0-2A, 0-70V @ 0-1A, and 0-200V @ 0-100mA, which could be selected by the user for testing. Meanwhile, the voltage can be outputted in either a triangle wave or DC for measuring leakage, although this mode also decreases the maximum current by 50% to prevent overheating. Beyond the basic three ranges is a dial for setting six current dividers that can further reduce the maximum current by a set multiple, such as 0.5, 0.2, all the way down to 0.02.
Generating steps
One of the most important parts of a curve tracer is the step generator, which produces the changes in input current/voltage for the device under test (DUT). It uses a 555 timer to delay each step by a certain number of milliseconds based on the delay set by the user. From here, it allows the incoming signal pulses to increment a counter with four output pins for a total of 0-7 steps. When all of the steps have been cycled through, a binary-coded-decimal to decimal decoder IC resets the current step back to 0. The last control circuit contains a complex network of capacitors, resistors, and transistors, which select what the final output voltage/current should be.
Power delivery and safety
Because this DIY testing equipment is meant to be plugged directly into mains power, safety was a large priority. If a fault on one of the output pins is detected, power to the pins is quickly stopped and does not resume until the fault is no longer present. High voltages, faults, and mains power all have their own LEDs on the front panel in order to indicate potential dangers to the user.
Fabrication and assembly
After carefully designing his circuits, Versteeg sent off the schematics and had several PCBs made for each part of his curve tracer. The front and back panels might seem like just another plastic piece at first glance, but they are actually circuit boards with components on the back and holes cut out for dials and switches. In addition to these, the front panel has a secondary back plane with even more components, while the power management PCB is mounted securely to the base of the device. You can read more about Versteeg's project here on his blog.