In our final installment of Tools of the Trade (with respect to circuit board assembly), we’ll look at how the circuit board is tested and programmed. At this point in the process, the board has been fully assembled with both through hole and surface mount components, and it needs to be verified before shipping or putting it inside an enclosure. We may have already handled some of the verification step in an earlier episode on inspection of the board, but this step is testing the final PCB. Depending on scale, budget, and complexity, there are all kinds of ways to skin this cat.
In the last episode, we put our circuit boards through the reflow process. Unfortunately, it’s not 100% accurate, and there are often problems that can occur that need to be detected and fixed. That’s what the inspection step is for. One could insert an inspection step after paste, after placement, and after reflow, but the first two are icing on the cake — the phase where most mistakes can be caught is after reflow.
There are a number of problems typical with a surface mount reflow process: Continue reading “Tools of the Trade – Inspection”
If you’ve played around with laser diodes that you’ve scavenged from old equipment, you know that it can be a hit-or-miss proposition. (And if you haven’t, what are you waiting for?) Besides the real risk of killing the diode on extraction by either overheating it or zapping it with static electricity, there’s always the question of how much current to put into the thing.
[DeepSOIC] decided to answer the latter question — with science! — for a DVD-burner laser that he’s got. His apparatus is both low-tech and absolutely brilliant, and it looks like he’s getting good data. So let’s have a peek.
First up is the detector, which is nothing more than a photodiode, 100k ohm load resistor, and a big capacitor for a power supply. We’d use a coin-cell battery, but given how low the discharge currents are, the cap makes a great rechargeable alternative. The output of the photo diode goes straight into the scope probe.
He then points the photodiode at the laser spot (on a keyboard?) and pulses the laser by charging up a capacitor and discharging it through the laser and a resistor to limit total current. The instantaneous current through the laser diode is also measured on the scope. Plotting both the current drawn and the measured brightness from the photodiode gives him an L/I curve — “lumens” versus current.
Look on the curve for where it stops being a straight line, slightly before the wiggles set in. That’s about the maximum continuous operating current. It’s good practice to de-rate that to 90% just to be on the safe side. Here it looks like the maximum current is 280 mA, so you probably shouldn’t run above 250 mA for a long time. If the diode’s body gets hot, heatsink it.
If you want to know everything about lasers in general, and diode lasers in particular, you can’t beat Sam’s Laser FAQ. We love [DeepSOIC]’s testing rig, though, and would love to see the schematic of his test driver. We’ve used “Sam’s Laser Diode Test Supply 1” for years, and we love it, but a pulsed laser tester would be a cool addition to the lab.
What to do with your junk DVD-ROM laser? Use the other leftover parts to make a CNC engraver? But we don’t need to tell you what to do with lasers. Just don’t look into the beam with your remaining good eye!
Hardware hackers love their test equipment. There are entire forums dedicated to talking about multimeters, oscilloscopes, signal generators, and other common bench tools. At times it seems we spend more time talking about our tools than actually using them. For some, off the shelf equipment is never quite good enough. These hackers, makers and engineers design and build their own test equipment. This week’s Hacklet is dedicated to some of the best test equipment projects on Hackaday.io!
We start with [Roman] and Handheld Electronic Test And Measurement Lab. [Roman] travels a lot, and often needs to bring a lab’s worth of tools with him. After suffering through several ‘random’ searches, he decided to design a simple tool that would cut down his packing, and not get him strip searched. The handheld lab packs a multimeter, low-frequency oscilloscope, data logger, waveform generator, and several other tools into a small package. The tool can be connected to a PC to display data and update settings. The on-board PIC24 handles all the hard work of taking measurements. Some careful analog design gives this tool 10 megohm of input impedance.
Next up is [Jaromir Sukuba] with 10$ curve tracer. The only way to find out of that a transistor or diode really works as well as the data sheet suggests is to pull out your semiconductor curve tracer. Curve tracers are also perfect for matching transistors for projects like analog synthesizers. [Jaromir] built this quick and dirty tracer over the course of just two evenings. A dsPIC microcontroller runs the show, generating an IV curve by sending pulses through the device under test. Once the curve has been traced, the PIC displays the results on a TFT LCD module. The tracer is a bit limited with a max of 35V at 0.5 amps. Knowing [Jaromir] though, extending the range would only take another evening or two of work.
Next we have [Jithin] with A Versatile Labtool. This tool can do just about everything you could want – all in one box. From oscilloscope to frequency counter to multimeter to current source, and much more. Much like [Roman] up above, [Jithin] chose a Microchip PIC24 MCU as processing heart of his design. The Versatile Labtool connects to a PC via USB. If you’re not close to your PC, an ESP8266 module allows the unit to connect over WiFi. A PC isn’t required though. The on-board OLED is always available for quick measurements.
Finally we have [ZaidPirwani] with Engineer’s Multi Tool, his entry in the 2015 Hackaday Prize. [Zaid] started with the popular transistor tester codebase. He ported the code to his own hardware, an Arduino Nano and Nokia LCD. Making the port function required quite a bit more work than [Zaid] expected. He ended up going with a fresh repository and adding a bit of code at a time. Once everything was working, [Zaid] verified that his hardware design operated as expected with a good old-fashioned multimeter. Now that everything is working, [Zaid] is just about out of space on the little ATmega328. Next stop is a Teensy 3.2!
A special thank you goes out to [Jaromir Sukuba] for suggesting test equipment as the theme for this week’s Hacklet. You can find his projects and more on the new test equipment project list! If I missed your project, or if you have a suggestion for a future Hacklet theme, don’t be shy! Drop me a message on Hackaday.io. That’s it for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of Hackaday.io!
A time domain reflectometer, or TDR, is an essential piece of test gear when working on long cables. The idea is simple: send a pulse down the cable and listen for the reflection from the far end. The catch is that pesky universal constant, the speed of light.
The reason the speed of light is an issue is that, in a traditional system, the pulse needs to be complete before the reflection. Also, time is resolution, so a 1 GHz sampling rate provides a resolution of about 10 centimeters. [Krampmeier] has a different design. He sends variable length pulses and measures the overlap between the outgoing and reflected pulses. The approach allows a much simpler design compared to the traditional method.
You may think you’ve built a power supply for your bench. Heck, we all do. But until you check out [Denis]’s bench power supply build, you may not even know what you’re missing.
[Denis]’s design is nearly entirely modular and targeted to the intermediate builder. It’s built on easily available parts and through-hole components. It’s got an Arduino running as the brains, so you’re going to be able to hack on the code when you feel like tweaking it. But easy doesn’t mean light on features. Let’s walk through the build together.
It starts off with a pre-regulator: a switching MOSFET that gets the voltage down to just a couple volts above the target value. Then it’s off to the post-regulator that includes all of the fine adjustments, the DAC and ADC interfacing to the microcontroller, and some fancy features like a “down-programmer” that turns the output off extra quickly.
On the user end of things, [Denis] made a very sleek board that incorporates a TFT touchscreen for the controls, Arduino connections, and the obligatory banana plug outputs. There’s opto-isolation on the SPI bus, a real-time clock, and a bunch more goodies on board. He’s in his third revision of this module, and that level of refinement shows. It’s even SCPI compliant, meaning you can control remotely using an industry-standard protocol.
So what would you do with a ridiculously fancy power supply under microcontroller control? Test out battery charging algorithms? Program test routines to see how your devices will work as their batteries drain out? We have no idea, but we know we want one!
If you work on RF circuits–even if you aren’t a ham radio operator–you ought to have a dummy load. A dummy load is a non-radiative “antenna” with known impedance that you can use to test your RF circuit without radiating. For radio work, you usually just need a 50-ohm resistor that is non-inductive (at least at the frequencies you are interested in) and that can dissipate the amount of power you’ll expect it to handle (at least for a short time). [VO1PWF] wanted a dummy load and built his own.
The Cantenna (not the Pringle’s kind; see left) was a famous dummy load design when Heathkit was in business. It was a single carbon rod immersed in a paint can full transformer oil (which we now know was full of dangerous PCBs; and we don’t mean printed circuit boards). [VO1PWF’s] design is a little more practical, using some resistors in parallel (20 1K resistors), a plastic pipe housing, and mineral oil to keep it all cool.
The reason for the parallel resistors is to maximize the power handling capability. The resistors are 3W units, so the dummy load–in theory–can handle 60 watts. Often, high power resistors are wire wound and thus have a good bit of parasitic inductance that makes the dummy load reactive (not a good thing since that makes the load impedance vary by frequency). They do make non-inductive wire wound resistors, but these aren’t truly non-inductive. The wire winds in two different directions, so the inductance tends to cancel out. We wouldn’t trust them to be a pure resistance in a high-power dummy load design.