New & Reviewed

Built & Tested: Comprehensive LED Tester Kit

Daniel Koch

Issue 50, September 2021

The most versatile and comprehensive LED tester we have ever seen, and you get to build it too!

This LED tester from LEDsales can test two-, three-, and four-pin LEDs at a variety of currents, has a voltage display so you really know what’s going on, and can even test RGB LEDs with one, two, or three colours at once by flicking a switch.

We all have something or things in our lives that just excite us for reasons we cannot explain. Some like a certain food, others just like a certain type of car. For makers, often it's a new piece of test equipment or tool.

For me personally, I miss the days where board-and-component level kits where you had to place and solder everything yourself were the standard. Don’t get me wrong, I love the developments in the maker world, like the many pre-made modules and the amazing projects we see made with Raspberry Pi or Arduino. Some of these are built in the from-scratch vein, too, with dedicated PCBs and clean, crisp layouts. However, there is just something pleasing about a well-engineered circuit board-based kit with neatly-aligned components reliably soldered down for years of trouble-free running.

This kit from LEDsales is the best of both worlds: It’s a well-designed, neat-looking kit, of a piece of test equipment. Most makers have seen LED testers, and quite a few of us own one. They can be had pre-made for less than $20 from Altronics, with a ZIF socket, or Jaycar for under $14 with a header socket. Both the mainstream retailer offerings feature a series of current options, with a maximum of two channels at each current.

Q2010 LED Tester from altronics.com.au

The Jaycar one even has a ‘battery indicator’ LED in the panel, which lights up when there is an LED connected even if it’s reverse-biased (a handy feature to know if the contacts are bad or if it’s the LED that’s the problem). However, the LEDsales kit is far and above in a class of its own.

AA0274 LED Tester from jaycar.com.au

FEATURES

SINGLE COLOUR SECTION

The LEDsales kit can test standard LEDs at 1mA, 2mA, 5mA, 10mA, 20mA, 25mA, and 40mA. However, there are six 10mA channels and eight 20mA channels, so you can compare a lot more LEDs side by side. This is far better than the maximum two channels we have seen on other designs. These rows all have resistors based on an LED forward voltage of 3V, which is pretty common.

RGB SECTION

Further, it can test four-pin RGB LEDs in both common anode and common cathode configuration, a feature which we have not seen before. It can also test the square Superflux-style LEDs, both single-colour and RGB versions. In both RGB options, there are four switches in play: One switches between common cathode (CC) and common anode (CA), while three control each separate colour. This clever feature allows testing of the individual dies in the LED, individually or in combinations of two as well as all. You can even fit two RGB LEDs side by side! However, they will have to be both CC or CA to get a result from both. This is really useful if you want to compare the colour of two different RGB LEDs. This whole area has resistors selected based on a forward voltage of 3V and a current of 10mA per chip, giving a total of 30mA per LED, as the most common middle-ground values.

MASTER CONTROLS

In the middle of the front panel, an illuminated pushbutton switch and a micro paddle switch sit side by side. The pushbutton is the test button, and it illuminates when there is a test current available. In other words, it will light when current is applied to the test area, whether or not an LED is correctly fitted into any of the sockets.

This confirms the tester is working, but the paddle switch is an override. Toggling it to the ‘on’ position locks the tester on, and an LED will light as soon as it is applied, correctly oriented, to the relevant testing sockets. However, leaving this switch ‘off’ means that current is only applied to the test LED when you want it to be. This allows you to correctly orient and seat high-brightness LEDs before making sure they’re pointing away from your eyes when you light them up.

VOLTMETER

This is another great addition to the LEDsales kit. At the bottom of the front panel, there is a three-digit LED display. It has its own on/off switch, too, so you can deactivate this feature if you really want to max out the battery life. When switched on, the meter will display the battery voltage whenever the ‘Test’ switch or button is on. Because the LED display draws a similar current to the LEDs under test, it’s not a bad approximation of battery voltage. When an LED is being tested, you will see the voltage drop and this is particularly true at higher test currents. This is just the nature of 9V batteries, which generally have low current capacities.

However, that’s not all the voltmeter does. The main reason for its inclusion is that using the single-colour ‘Superflux’ test area, which cleverly has three rows so normal 2.54mm (most LEDs) as well as wider 5.08mm (superflux, bent-lead, and other LEDs) spacings can be tested. The voltmeter shows the voltage drop across the LED. This is a very useful diagnostic tool, especially as some red LEDs can have a Vf of as low as 1.5V. That may influence your resistor choices if you like the brightness from, say, the 10mA channel in the top header, but find your LED has a Vf of 2V, not the 3V that those currents are calculated for.

As if that were not enough, the voltage drop of regular diodes can be measured. This allows you to determine if they are SSR or Schottky, and whether they are good or failing. You'll also find the polarity quite easily, if case markings are unclear or faded.

IT’S A KIT!

While all of that is a great set of features, the most exciting thing for me was the fact that it’s a kit! It’s a very well put together kit, too. On opening the mailing box, we unwrapped the package to find a set of bags inside a main bag. All of these bear LEDsales’ closure stickers, which informs that the bags are made of genuine cellophane, not plastic derived from crude oil. That’s important for us at DIYODE, because we try to reduce our waste footprint where possible. Genuine cellophane is made from cellulose, a plant fibre, and is naturally antistatic and biodegradable. That’s biodegradable, not just ‘degradable’. Every little bit adds up!

Once opened, the kit layout was pleasing. A selection of tiny 1/8W sized (see below) metal film resistors, some headers, a bunch of switches, the voltmeter, and assembly hardware matched with three very well-finished, silk-screened and coated PCBs. The main one is plated through and double-sided, so when you solder it, allow slightly more time than you normally would with the soldering iron in contact with the join after solder is first seen to flow: Chances are, you’ll see the solder wick down through the plated hole and you’ll need to top up the join.

As far as components, LEDsales have not gone cheap. Though 1/8W sized, the resistors are 0.4W Vishay or Royal Ohm brands, except the 3k, which is a 0.4W Philips. The headers are CONNFLY DS1023-1 series, which have good long-term reliability and lack the tendency of the cheap ones to lose their springiness. Even the switches are of good quality, and in fact finding ones that are up to the high standard was what kept LEDSales from producing this kit earlier.

The instructions for the kit are available digitally, and a slip of paper with the kit directs you to the right web page and provides a QR code. The instructions are very comprehensive, and give a good operational and circuit description as well as clear assembly instructions. Few details are missed, but there are a couple of additions to suggest, which I’ll include as I go through the build.

FIRST STEPS

As with any well-designed kit, the instructions direct you to start with the lowest profile components, which in this case is the resistors. The builder is even directed to be careful bending the leads of these, as they are bent very close to the case. The only additional caution I would add is to align the resistors. While not polarised, having resistors aligned so that all colour codes read left to right for horizontal and top to bottom for vertical alignments makes future identification and fault-finding much easier.

That’s even more true of these tiny resistors, which have minimal space between colour bands, little to no extra space on the tolerance band, and tiny colour bands to boot. Values can be hard to read when brand new, and it gets worse as the colours age. The instructions point out that using a multimeter to check values is a good idea, and we used our Peak Atlas LCR meter for the task.

Next up is the headers. The instructions are clear about this, and it helps to follow them well. The builder is directed to install the largest header, then use this to align the remaining headers and the paddle switches with the lower PCB so they sit well in the front panel. However, I still found this a challenge. Instead of holding the front panel, I temporarily fitted the standoffs that later mount these two PCBs together, and installed the front panel screws. Then manipulating the two PCBs together was much easier, alignment was maintained, and I was able to solder the switches. I ended up using our PCBite helping hands to hold the solder so that I could hold the boards in one hand with a finger securing the switch where I wanted it, and my other hand for the soldering iron. Note that at this stage, only two pins of each header or switch are soldered.

Note that in the photo, I'm actually soldering the pushbutton from a subsequent step, so the front panel is not fitted.

Once all the headers and switches are aligned with two pins soldered, go back and solder the remaining connections before removing the front panel and standoffs. The instructions clearly say that the pushbutton switch has a mark on the cathode pin of the LED that illuminates it, and to check with a battery and resistor if in doubt. The mark on ours was red, which is usually of course to denote positive, or anode. A check with a resistor and 5V power supply revealed that in fact, this was the cathode. The red ink must have been whatever the manufacturer switch manufacturer had at the time. With the pushbutton switch installed, the instructions gave hints to help mount the voltmeter as well. That done, the battery holder is fitted and the main PCB is complete.

Before fully assembling the tester, the instructions call the builder to test it. Though tempted to have too much confidence and skip this step, history came to mind and I decided to comply. This process is straightforward, but will be helped along if you happen to have a superflux single-colour, superflux RGB, and a standard package RGB LED handy as well as a regular single-colour standard package LED. Even if you only have a basic LED, you can still test all of the functions, just move one of the LED legs around in the four-pin sockets to check your solder work. That done, follow the instructions to assemble the case, and you’re done! The dome nuts that secure the back panel even act as feet.

The final words from the instructions are some suggestions, and one regards a battery choice. Replacing the 9V battery involves removing the back panel. A lithium battery in a 9V package with USB charging port is recommended, and LEDsales have given an example of a brand that is available. They do not sell this item, so this isn’t self-promotion. It’s just a sensible way to make use of the open-frame design.

EXTRA FEATURES

The back panel of the unit is worth mentioning. It has, screen printed on the face, a 60mm ruler, resistor colour code chart (monochrome, so text rather than colour swatches), and a table explaining 3-, 4-, 5-, and 6-band resistor colour codes. There is also a diagram for identifying anode and cathode (+ and -) connections on LEDs, and a list of websites with good LED resources, including a resistor calculator.

Additionally, the last page of the instructions provides a very useful table showing the actual versus nominal currents for a measured range of LED forward voltages. This will be very useful to those with current- or voltage-critical devices or situations, and is a nice touch from the designer. Of course, this originates in the fact that any current calculation for the channels has to assume a forward voltage, because fixed resistors are used.

CONCLUSION

All in all, the LED Tester kit from LEDsales outperforms its price tag. It’s a well-designed kit, easy to put together, with high-quality PCBs and great supporting instructions. It's a highly functional finished product which the whole DIYODE team thinks is well overdue in the market. Why we all put up with standard LED testers all these years is beyond us! Thanks to LEDsales for sending us one, and the LEDsales website is well worth a browse, too. We find a lot of great items there that make it into our projects from time to time.

Shopping List

Available from LEDsales

  • Multi-function LED Tester Kit LED_TEST_KIT Introductory price $28