After several breadboard projects, wisdom of the productivity gurus becomes very believable, 25%-30% of working time involves looking for misplaced or poorly identified items. The usual advice, “use a filing system”, doesn’t quite to apply to the breadboard practitioner.
It seems regardless of all good intentions and resolutions, the management of the common 2-pin LED demands great organizational skills and a steadfast habit of tidiness. For those that may be short on this standard, the acquisition of 100x Red-Green-Blue-Yellow-White emitted colour LEDs (clear lens) quickly presents a challenge.
After 100 or so LEDs are set free, the difficulty begins simply with identifying which of the five emitted colour will be put forth by a LED. It is further complicated by the ‘non-function’ category that may result from some misadventure with wrong voltage, poor resistor identification or poorly handled jumper wires.
The simple question is how can emitted colour LEDs be sorted/selected and QC’d. There is the breadboard itself, temporary and already implicated in the risk of misadventures. The concept of a standalone solution housed in a decorative metal case is largely delusional. The middle ground is of course another breadboard gizmo.
The ambition for this Instructable is to show a practical Caddy for testing, sorting and selecting 2-pin emitted colour LEDs.
The Instructable Breadboard Friendly Tactile Switches should be kept close at hand. The dialog and images for the technique of construction are excellent.
Step 1: Material
For this project the following items or a facsimile of choice are required:
- 1x - Piece of Prototyping Board.
- 1x - Single Row Male Pin Header (4-pins)
- 1x - Single Row Female Header Socket (4-pins)
- 1x - Male Double Row Pin Header Strip
- 1x - Female Double Row Socket Strip
- 2x - Radial Resistor 820Ω 1/2W
Step 2: Design
In considering the layout of the Caddy, two features came to mind. The first is obvious; a pair of LEDs should be mounted at the same time. There seems to be some noticeable variation in the physical characteristics of LEDs, it is a bit easier to sort when these can be displayed side-by-side.
The other is the arrangement for use as a parallel circuit or as pair of a common anode or common cathode LEDs. The schematic shows J1 as the common terminator. For a parallel circuit, J2 is inserted in the power or ground strip and a single jumper wire to J1 completes both circuits. Maybe the scenario for testing/sorting/selecting?
The Caddy can be used to operate a pair of common anode or cathode LEDs by inversing J1-J2. J1 is inserted in the power or ground strip and the sides of J2 independently connected with a source/sink through the breadboard matrix.
The value for the radial resistor comes more from the expected application than an exact specification. The 1/2W rated, 820Ω resistor will handle a 12V source/1V forward voltage without exceeding 15mA, conditions that could be encountered in older (non-emitted colour) IR components. A value of 1K2 Ω would give a wider safety margin but would not be as desirable when used with the 5V common to Arduino and breadboards. Indeed at 5V the LED current is a retina saving 3-5mA for the emitted colour products most likely to be encountered.
Step 3: Preparation and Soldering
The prototyping board needs to be 6x6 holes. To provide a small hold for a ‘third-hand’ or alligator clip, the image shows a 7x7 grid and edge material. It should not be too difficult to trim most prototyping board.
The sequence of soldering of the components is not critical however the intent was to employ the leads of the radial resistors to create the ‘wiring’ shown by the colour red in the schematic. Therefore the 820Ω resistors were the first components soldered to the prototyping board. The radial leads were then shaped and trimmed to match the related solder points
Refer to Step 4 of Breadboard Friendly Tactile Switches for the details of soldering the header pins (J1&J2). The female double row socket strip is used in lieu of the two female headers for alignment. The leads of the radial resistor are overlapped and soldered to both pins of J1.
Use the same technique of Step 4 to solder the 2-pin female sockets (H1&H2) but use the male double row pin header for alignment. The lead of the radial resistor is soldered to only one pin at each location.
Finally, each side of the single row male pin header J2 is soldered to the unused pin of H1&H2. Drag soldering is possible however a small piece of discard component lead is used here to create ‘wiring’ shown by the colour black in the schematic.
Step 4: Summary
The Caddy is a project that turned out better than expected with the accompanying regret that more care wasn’t taken in its fabrication (and for an Instructable documentation). Probably because the sockets are elevated and employ a less aggressive spring clip, the LED is quite easily inserted and extracted. The point for insertion is an unambiguous pair of sockets that are spaced correctly for the ‘mint condition’ component.
Of course ‘better than’ is quite distant from ‘perfection’. A notable irritation, unlike Eric Brouwer's Friendly Tactile Switches, the Caddy does not stand stable when off the breadboard. Experimenting with alternate layouts could be a project for some inclement winter evening,