How to Construct a Micro Interface Using Perf Board

Rev 1.1 -- 28 April 2001 -- Tommy N. Tyler

1. INTRODUCTION. These instructions show how to build the Micro Interface using a 1" x 1.3" piece of perf board. Instructions for an easier method of construction using a PCB are contained in the file MicroPCB.zip, and instructions for just "floating" the IC in the space inside the connector hood are contained in the file MicroClassic.zip. It is suggested that you read through these instructions completely before starting construction. Most of the interconnections can be made with the resistor and capacitor leads themselves, or the cut-off remnants of them, often by routing them in and out through the same holes occupied by the IC pins, like a needle and thread. The fit is pretty tight using Radio Shack perf board, which has .042" diameter holes. Some members have anticipated this by drilling out the 14 holes occupied by the IC leads with a 1/16" diameter drill before starting. Others have just used an Exacto knife to enlarge holes where necessary. Either way, just be sure to use wire no larger in diameter than the resistor or capacitor leads and you shouldn't have a problem placing both an IC pin and a wire through the same hole.

2. PARTS REQUIRED. Although not listed below, you will need a 6-pin JP1 mating connector with cable. Various sources and methods of making this (such as sawing off a piece of IDC connector from a discarded IDE disk drive cable assembly) are described elsewhere.

ITEMQTYDESCRIPTIONRADIO SHACK PART NO.
11About 2 sq. in. of Perf Board 276-139X
21IC, 74HCT125 or 74HC125 276-2825
33Resistor, 1K 1/4W 271-1321
41Resistor, 100K 1/4W 271-1347
51Capacitor, 0.1uF 50V 272-109
61DB25 Male Solder Connector 276-1547
71DB25 Connector Hood, Metal 276-1510

Note: 276-1549 and 276-1536 connector hoods are too small for the perf board

3. PERF BOARD PREPARATION. Cut and notch the board as shown in Figure 1 below. Perf board breaks fairly easily in a straight line if you first scribe both sides along the center of a row of holes with a sharp knife. Clamp the board near the scribe line in a vice or pliers or lay it along the edge of a table to break it. You can also use a modeler's saw or motorized Dremel tool to cut out the board shape. Be careful when making the corner notches because the phenolic board material is very brittle. Practice on scrap board to develop a method that works for you.

Figure 1. Cutting and Sanding Perf Board to Size

Using sandpaper laid face-up on a flat surface, or a file, smooth all eight sides down to the point where the edges of the holes are barely visible. This is necessary for the board to fit within the hood. Check to make sure the board fits inside the hood before you start assembly.

 

4. ASSEMBLY. Install integrated circuit U1 as shown in Figure 2 below. (There is not enough room inside the connector hood to accommodate an IC socket.) Note: Orientation of the resistors and capacitor is not critical (they are not polarized), but U1 must be placed precisely as shown. Press U1's pins flat against the back side of the board. Note that some pins are bent inward and some outward.

Figure 2. Installation of Integrated Circuit U1

 

Insert resistors R1, R2, and R3 as shown in Figure 3 below. (Note: These are 1K resistors, color coded Brown-Black-Red, followed by a gold or silver band.) Bend the leads at the bottom end flat against the board and leave them hanging out over the edge. Solder the other lead of R2 directly to U1-2. Pass the lead of R3 up through the hole of U1-4 before soldering it there. Do not cut this lead.

If the lead of R1 is not long enough to reach U1-13 you must use a short piece of resistor lead wire as a jumper. A handy way to hold the jumper in position while you solder it is to stick the ends through unused holes, then cut them off flush with the top of the board after soldering.

 

Figure 3. Installation of Resistors R1, R2, and R3

 

 

Route the resistor lead that comes up through the hole of U1-4, back down through the hole of U1-1, as shown in Figure 4 below, and solder it to U1-1. Cut off the excess lead. Make sure the loop on the top side of the board doesn't touch pins 2 or 3 of U1.

Figure 4. Connecting U1 Pins 1 and 4

Insert resistor R4 as shown in Figure 5 below. (Note: This is a100K resistor, color coded Brown-Black- Yellow, followed by a gold or silver band.) Bend one lead back and solder it to both U1-9 and U1-11. Bend the other lead so it touches U1-14 and cut it to length, but do not solder it yet.

Figure 5. Installation of Resistor R4

Insert capacitor C1 as shown in Figure 6 below. Cut one lead so it just reaches U1-14 and R4, and solder all three leads together. Route the other lead up through the hole for U1-12, then solder it there.

Figure 6. Installation of Capacitor C1

Route the lead of C1 back down through the hole of U1-10, as shown in Figure 7 below, but do not solder it there yet. Make sure the loop on top of the board clears U1-11.

Figure 7. Connecting U1 Pins 10 and 12

 

Continue routing the capacitor lead across U1 and up the hole of U1-5, as shown in Figure 8 below. Solder both U1-5 and U1-10.

Figure 8. Connecting U1 Pins 5 and 10

 

Finally, route the capacitor lead back down through the hole of U1-7, as shown in Figure 9 below, making sure it clears U1-6 above the board. Solder the lead to U1-7 and cut off the excess lead, if any.

Figure 9. Connecting U1 Pins 5 and 7

Solder a bare jumper wire to U1-8 and route it as shown in Figure 10 below. The jumper must be at least long enough to reach the lower edge of the board.

Figure 10. Installation of Jumper Wire to U1-8

 

Slide the board in between the solder tails of the connector pins, as shown in Figure 11 below. If you want to hold the board in place while you solder the wires to the connector, run a small wire through an empty hole in the front row, loop it around the connector and twist it to pull the board tightly against the connector. The wire can be removed later after a few solder connections have been made. You will be able to adjust the position of the board slightly to center it after all assembly has been completed.

Cut the wire from U1-12 to length and solder it to connector pin 21.

Figure 11. Attachment of Board Sub-Assembly to DB25 Connector

On the bottom side of the board, cut the leads from the three resistors R1, R2, and R3 to length and solder them to connector pins 2, 3, and 4, as shown in Figure 12 below. Cut the loose end of the jumper wire to length and solder it to connector pin 11.

Figure 12. Connections to DB25 Connector Pins 2, 3, 4, and 11

 

 

 

That completes the assembly of board and connector. This is a good time to inspect your work carefully. Make sure the top and bottom sides look like Figures 11 and 12, that all solder joints are bright and shiny (no cold solder joints), and that none of the bare wires are touching adjacent contacts or other wires.

 

 

Figure 13 below shows how the cable is attached to the board. Use a cable no longer than six feet. The illustration shows two alternatives, one using an IDC (Insulation Displacement Contact) connector with ribbon cable, and the other using a solder type connector with a multi-conductor cable or a bundle of separate wires. Many other combinations are possible. In any case it is critical that the wires from the six connector pins be connected according to the numbers along the edge of the board. Note the detail illustrating the six pins inside a remote control as you look down on them through the battery compartment. If you do any continuity testing to verify which wires are connected to which pins, use a 1/4 watt resistor lead wire as a probe to insert into the connector contacts as a probe. Anything larger may damage the contacts.

Lay the end of the cable over the board and cut the wires to the approximate lengths for them to reach their attachment points. Then strip the insulation back about 1/10" and apply a small amount of solder to each wire.

Drill the six holes along the edge of the board just large enough for your cable wires to slip through them. This will provide a good enough strain relief that nothing else is required. Pass the cable wires through the holes and solder them to the appropriate points as shown. In most cases all that's necessary is to hold the end in position while you reheat an existing solder joint.

Adjust the cable wires so they are all pulling uniformly where they zig-zag through the board. That way they all share the strain if the cable is pulled. Leave any excess wire length inside the connector hood. Whether you use the cable clamp strain relief supplied with the connector hood, or some other means of supplimentary strain relief, is optional.

 

 

Figure 13. Attachment of Cable to Board

 

Place the board assembly in the connector hood, as shown in Figure 14 below and you're done.

 

Figure 14. Final Assembly

 

 

5. TESTING. The easiest and safest way to test the interface is to plug it into a remote, WITHOUT BATTERIES IN THE REMOTE, and try a memory download using either the Windows "IR.exe" software or the older DOS "dremoteif.exe" software. A handy feature of the Micro interface is that you can use it to upload and download the remote's memory without even installing batteries. The computer will supply the tiny amount of power needed. The only thing you can't do without batteries is transmit a command from the remote. Once you're sure the interface is working properly go ahead and install the batteries. You can upload and download files, then operate the remote, all without unplugging the interface. Don't worry about draining your batteries. You can leave the interface plugged in all day long. It draws negligible current.

Note that your interface may randomly fail the "check" in IR.exe even though there is nothing wrong with it, so that test is not recommended as a means of determining whether the unit is faulty. If the no-battery memory dump test fails there's a file in the Interface Designs section that provides more comprehensive information on interface testing.

As a precaution against corrupting the EEprom contents it is recommended that you turn on your PC before plugging in the remote, and unplug the remote before turning off the PC.

 

 

 

 

6. SCHEMATIC. A schematic of the interface is shown in Figure 15 below for reference. It is similar to the buffer portion of previous interface designs except that C1 has been added in consideration of the distance between U1 and its power source.

Figure 15. Schematic

 

 

 

7. REVISION HISTORY. This revision 1.1 of these instructions differs from previous versions as follows:

  1. The sequence of construction has been changed so that all wiring on the board is completed before the board is attached to the DB25 connector.
  2. Resistor R4 has been added to make the circuit consistent with that of the PCB version.
  3. Details of wiring the cable are enhanced, and six wires are shown rather than five.
  4. Testing information has been added.
  5. Text and illustrations have been integrated to make the instructions easier to follow and more concise.

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