MEP EP#294: Twisted Pairs

09/15/21 • 46 min

USB vs Ethernet for Test Equipment?

How to make hardware work with Ethernet?

Tag Connect : Edge-Connect

Bias test connector - OTC (one time connect)

PEM smtsss-4mm-6et solderable spring standoffs
Use in conjunction with through hole pogo pins
Just add holes and target points on main pcb and plug the connector in for access to the nets

USB vs Ethernet for Test Equipment?

How to make hardware work with Ethernet?

Tag Connect : Edge-Connect

Bias test connector - OTC (one time connect)

PEM smtsss-4mm-6et solderable spring standoffs
Use in conjunction with through hole pogo pins
Just add holes and target points on main pcb and plug the connector in for access to the nets

Metrology and You

Do I need to worry about all of this? (as a hobbyist, is accuracy important?)-
Measure with micrometer...
Taking Measurements
- voltage, current, resistance, inductance, capacitance, Q, frequency, time, noise, RF/microwave
- Measurement Uncertainty
  - +/- 0.1dB specification - what can go wrong?
How do you make things more accurate?
- System engineering - when the boards are put together, does the system work?
- Testing the idea that multiple resistors are tighter tolerance than single
  - Are the values random?
- Sources of errors - narrow things down to the path between a sensor and an ADC
  - Temperature
  - Noise, thermal
  - Noise, switching power supply, rectifier diodes
  - Noise, clock, data, address
  - DC shift - where does the ground current flow? Screws, contact resistance, and X-Acto blades.
- Offset voltage and current
Connector Repeatability
Temperature
- Repeatability/Skid
- Controlling temperature (room air, coffee cup, fingers, oven proportional control)

The DFs

How to DFX

Identify what you are Designing For
- Perhaps list them based on priority
- Make a list of all of the items
- Make a timeline for which DF applies when in the product life
Create a list of key design criteria
- This will vary based on where the product is in the design cycle
Schedule specific focused time to have a team review the DF
- Have the main designer present, but it is best to have other perform the DF checks
Have a sign off and circle back process
- If it passes then have the team sign off and move to the next stage
- If it fails, have a process of fixing and asses if another full DF meeting is needed
- Perhaps just a small DF meeting to address one thing
At then end of the product design cycle you will have a folder of completed design checks that help validate the release of the product

DFA vs DFM vs DFP

Techniques for making revisions easier

Put circuits that you know need adjustment where you can reach them with a soldering iron or a probe
0 ohm resistors
- Make for very easy configuration changes
DNI/DNP - lots of people don't know this is a thing
Multiple footprints
Parallel components
Room for soldering!
Test points - different from component terminations
Keep lists of things to remove for production