EENG 393

In Lab 13 - Supply Chain

Requirements

There is no turn-in associated with this inLab. You may need some of the tutorials linked below to help with the asssmbly of your uSupply.

Objective

Case Study

Read the Sparkfun article about their purchase of a batch of counterfit ATmega328 chips.

Reflow Skillet

Hot Air Rework Station

Wire Tinning

Splicing wires

  • Make How To Splice Wires to NASA Standards
  • How to Mesh Splice

    Crimp tool with Dupont Connector

    JST connectors

    A wire harness is a collection of wires with connectors at each end. Wire harnesses are often a secondary consideration when designing a PCB, but in fact there is a lot to consider.
    Gender
    While the gender of some connectors is obvious, others can be confusing. Regardless, in order to make an electrical connection, you need a male connector plugged into its female counterpart.
    Polarity
    When a connector can only be positioned in one orientation to make a connection, it is said to be polarized. There are a lot of good reasons for polarized connectors, but they are often a little more expensive and less reliable than their non-polarized counterparts.
    Pitch
    The number of contacts per inch is called the pitch. Imperial units prevail in most circles with 0.1" being the most common.
    In this section we are going to walk through how to build a simple 4-wire harness to power your 556 timer PCB and gain access to the signals. There will be four main parts to our wire harness: To create a harness, you will need to attach the crimp to the wire using a crimp tool. The crimp connector has several opening to accommodate different gages of wire. My crimp tool has three openings, one to accommodate 24-28 gauge wires, one for 22-20 gauge and one for 20-18 gauge. My tool is ratchet, meaning that as the handles are squeezed together, the tool incrementally closes. Meaning that if the jaws are brought together to a certain distance, the jaws will remain there until the jaws are brought all the way together or the secret switch is pressed. The jaws are not uniform across their width. Close inspection reveals that both the upper and lower jaws consist of two plates. These two plates form two regions across the width of the jaws, a small side and a large side. When the jaws are fully closed, the small side of the jaws leave the smaller side opening smaller than the opening left on the large side. The first image below shows the small side of the crimp tool, while the second shows the large side.





    1. Strip 2-3mm of wire
    2. Position the crimp in the crimp tool - 3 clicks is enough to partially close the crimp tool and still have enough room to insert the crimp into the 28-24 opening.


    3. Insert the stripped end of the wire into the crimp tool. This is the msot difficult and critical step. I've found that while holding the crimp tool in my left hand, I can manuever my trigger finger on my left hand around and hold the female portion of the crimp into the small side of the crimp tool's jaw. You cannot alllow any portion of the female end to get in the crimp tool's jaw. At the same time, you need to insert as much of the crimp as you can into the crimp tool. Only when I am happy with the crimp position and my finger placement, do I turn the crimp tool over to look at the large side of the crimp tool jaws. I then insert the stripped end of the wire into the end of the crimp which is a few millimeters inside the large side of the crimp tool. You need to insert the wire so that the stipped wire is well into the inner wings but not into the female socket on the end of the crimp.


    4. Crimp and inspect - Once you have the crimp and wire positioned do you crank down on the handles. If you ahve done everything correctly you will get a sturdy crimp connection to the wire.


    5. Insert crimped wire into plastic housing


    You can remove the crimped wire from the harness by plucking up the barb on the plastic housing.