There’s a specific wiring problem that shows up whenever you build a multi-deck robot chassis: the Arduino is mounted on the lower level, but all the sensors live on the upper deck. You need to get a dozen or more signals — digital I/O, analog pins, 5V, ground — from one level to the other without creating a tangle of individual jumper wires flopping around. Order a ribbon cable breakout? Wait two weeks. Buy more jumper wire? You already have a pile of it.

Or you open your junk computer drawer and pull out an IDE hard-drive cable.

This is one of those hacks that’s almost too obvious once you see it: the flat ribbon cables that used to connect IDE hard drives to motherboards have 40 conductors on a 2.54mm pitch — the same spacing as standard Arduino jumper wires. The connectors on the cable aren’t quite the same shape as Arduino pin headers, but the jumper wire ferrules fit into an IDE connector firmly enough to use as a temporary (or permanent) connection point. A single cut-down IDE cable can route every digital pin, every analog pin, a 5V rail, and a ground from your Arduino up to a top-deck breadboard in one tidy flat harness.

The cost: whatever you were planning to spend on additional jumper wire. Replaced by zero dollars and the time to cut the cable to length.

This build is from 2012, when the channel was still MeanPC.com — same Lonnie, same garage, same workbench.

Why this works

Standard Arduino jumper wires use 2.54mm (0.1”) spacing, which is the same as the 40-conductor IDE/ATA connector. The fit isn’t locking — you’re not snapping the jumper into a latching housing — but the contacts are snug enough that the connection stays put with a little strain relief in place. In a robot chassis with tie-wraps holding the cable down, that’s plenty stable.

IDE cables come in a few varieties:

• 40-wire parallel ATA cables (older, flat grey) — 40 conductors, 2.54mm pitch. The one most people have in a junk pile.
• 80-wire Ultra ATA cables (sometimes grey/blue/black with a colored connector) — 80 conductors on a 2.54mm pitch, alternating signal and ground. Actually better — more conductors, every other one is ground — but the connectors are more densely packed.

For this build, a 40-wire cable gets cut down to expose a strip with 17 usable conductors on one side — enough for Arduino digital pins D2–D13 (12 pins), analog pins A0–A5 (6 pins), plus a 5V and ground. That accounts for essentially the entire useful pin complement of an Uno, routed in one flat bundle.

What you’ll need

• An old IDE parallel ATA cable (out of any pre-2010 desktop computer)
• Scissors and a craft knife or box cutter
• Tie wraps (zip ties) and Gorilla Glue or equivalent for chassis mounting
• A multimeter for continuity testing the completed harness
• Your robot chassis with an upper deck breadboard to wire to

No soldering required on the cable itself.

Preparing the cable

Cut the cable to a length that spans from the Arduino’s mounting position to wherever the top-deck breadboard will sit, with a few extra centimeters for routing. If the cable has three connectors (master, slave, and motherboard positions), cut it to keep one connector at each end — the connectors are where your jumper wires will plug in.

For a single-connector stub (one end connector, one cut end): fan out the cut end into individual conductors to plug them into breadboard rows. The ribbon is easy to split into individual wires by pulling apart the flat sections.

Count your conductors before mounting anything. A 40-wire cable gives you 40 conductors total. In this build, 17 were needed for the wiring plan described below. The cable was split lengthwise to keep only the 17-conductor section — cut parallel to the conductors, between them, so you get a narrower strip with clean edges.

Mounting to the chassis

Getting the cable through the chassis deck cleanly takes a bit of planning. The approach here: punch or drill a rectangular slot in the chassis deck, feed the cable flat through it, and then secure it with tie wraps and a dab of Gorilla Glue where it exits on each side. Gorilla Glue expands slightly as it cures, which locks the cable in place without relying on the tie wraps alone.

One thing to plan before gluing: battery compartment access. If the cable runs across the path you need to open to swap batteries, you’ll be unsoldering or cutting things later to change a battery pack. Route around any access panels before anything goes permanent.

Hot glue was tried first and failed. It doesn’t bond well to the IDE cable’s insulation and pops loose with any lateral stress. Gorilla Glue held.

Mapping pins to the breadboard

Once the cable is routed, the job is continuity-testing each conductor end to end and labeling where each one lands on the top-deck breadboard. A multimeter in continuity mode is the right tool — probe one end of a conductor, find the matching location at the other end, and mark it.

The mapping used in this build:

• Ground — first conductor mapped; tie to the ground rail on the breadboard
• 5V — second conductor; tie to the power rail
• D2–D5 — mapped first from the digital pins
• D12, D13 — mapped last on the digital side
• A0–A7 — all eight analog channels

One important note on D0 and D1: those are the Arduino’s hardware serial RX and TX pins. If your sketch uses Serial.begin() — for debugging, an LCD over serial, anything — using D0 and D1 for other signals will cause interference and can prevent the Arduino from uploading over USB. Leave those two pins off the harness or just don’t connect their other ends.

After all the conductors are mapped, every pin has a labeled column on the top breadboard. Plugging a component into A0’s column connects directly to the Arduino’s analog pin A0 without a separate jumper wire from top to bottom deck. The routing is already handled by the harness.

Reflections on this approach

This build approach has the feel of a prototype — or rather, the specific feel of the Apple I prototype, which Wozniak built with a similarly improvised aesthetic before anyone involved thought it was going to ship. The point of a breadboard-era robot isn’t aesthetic cleanliness; it’s iteration speed. Knowing you can get any Arduino pin to any sensor on the top deck without stopping to route a new jumper wire is a real productivity gain when you’re debugging in the evening and don’t want to wait on a parts order.

The honest thing to say about it: looking back, mounting the Arduino and the sensor deck as a single module — with the sensors directly above the processor on a tighter chassis — would have been cleaner from the start. The IDE cable works, but the neater solution is to not need the cable at all. Both observations are true simultaneously, and building the messier version first is usually how you figure out the cleaner version.

Tips for cleaner results

Label everything. Once the cable is mounted and the jumpers are in place, it’s impossible to trace which conductor is which by sight. A strip of masking tape along the cable with conductor numbers marked in pen saves a lot of continuity-probing later.

Mind the ribbon cable direction. IDE cables have a red stripe on one edge marking conductor 1. If you’re using both ends of the cable, verify that conductor 1 at the top end is the same wire as conductor 1 at the bottom — don’t assume the cable isn’t twisted.

Strain relief matters. The biggest failure mode for this kind of harness is pulling a conductor loose where it fans out into a breadboard. Tie the cable down close to where it terminates, so any pull on the cable is absorbed before it reaches the connection points.

Ultra ATA 80-wire cables are better for this, if you have one. The alternating ground conductors mean you can intersperse signal lines with returns, which reduces crosstalk on long runs and makes the cable more mechanically uniform. The signal pins are every other conductor, and you lose the alternating grounds but gain a quieter harness.

References and further reading

• ATA/IDE interface standard overview — Wikipedia article covering the 40-wire and 80-wire cable specs, connector pinouts, and the full history of the interface
• Arduino Uno pinout reference — official Arduino pinout diagram; the one to keep open while labeling conductors
• Arduino digital pin overview — explains the function of each digital pin, including the D0/D1 serial caveat
• Arduino analog reference — relevant if you’re routing analog pins A0–A5 through the harness
• Woz’s Apple I design notes — Computer History Museum archive; the prototype-first aesthetic isn’t an accident, it’s a documented philosophy