Electronics Design 101

Jeff Duval and Palash Nandy

Electronics Fundamentals

Get the Electronics 101 slides

Read Sparkfun’s electronics fundamentals

Here is what we are going to go over:

• Basic Electronic Components
• Ohm’s Law
• Kirchoff’s Laws [exercise: find i1, i2, i3]
• Circuit Simulation with SPICE
• Microcontrollers (in particular atmel attiny44)
• Input: push-button
• Input: Potentiometer
• Output: LED

At the end of this you should be able to design the circuit needed for homework

More stuff:

The slides also cover op-amps and power electronics. Very useful for the outputs week

This book: Horowitz and Hill, is the bible for electronics.

PCB Design

Get EAGLE CAD (sparkfun’s setup instruction)

Read Sparkfun’s PCB Basics and How to Read a Schematic

We will cover with a live demo:

• Circuit design process (schematic to layout)
• Creating schematic
• Wiring components together with nets
• Layout
• Exporting for milling

At the end of this part you should be able to create a millable file for your circuit

First time:

• Install EAGLE
• Add fab.lbr and fab.dru to eagle (see setup tutorial)

Each time:

• New schematic
• Add parts. Some common ones:
• fab/attiny44-ssu
• fab/res-us1206fab
• supply1/+5V
• supply1/gnd
• fab/resonator
• led/ledsmt1206
• use net to wire them together
• protip: move parts to check if they are connected
• save. Switch to board view (tiny plug/chip icon upper left next to 1/1 button)
• Drag components to where you want them to go
• use route (blue line icon) to connect components
• protip: Hit ratsnest (starburst) to check if everything is connected
• protip: Hit DRC (green check) to see if traces are millable
• drag dimension outline to be a snug fit around board
• type display none dimension into command box at the top to see outline.
• export as grayscale 600 dpi png for cutting out interior of board
• display none top to see traces
• export as grayscale 600 dpi png for milling traces
• go over to fabmodules.org to mill

More stuff:

See Jeff’s tutorial for more pointers

FAQ:

Q:Does the voltage divider (with two resistors) always provide the same voltage drop, regardless of the load/resistance on V_OUT? I suppose not, so how do we regulate this?

A 1):No. The rule of thumb here is to load the circuit with 10-20x more resistance. If you make your divider with 10k & 10k you shouldn't connect it to a load lower than say 100k.

A 2):Please note that even 10k & 10k is high for an ADC input. A cheap & simple trick is to place a small (say 10 or 100nF) cap in // with the lower resistor.

A 3):To keep this voltage independent of the load use a follower opamp

Q:Do we need 1 resistor per LED in parallel because otherwise, the current flow will be much higher in some LEDs than others (due to manufacturing variances, etc)? Or for some other reason?

A 1):Yes. If you look at the Current/Voltage curve of a diode (http://www.amperor.com/products/led/images/led_i_v_curve.jpg) you'll see that a slight voltage difference can create a huge difference in current.

A 2):What will happen if you // LEDs with only 1 resistor is that you'll destroy the one with the lowest voltage... then the second lowest... up to the point where they'll all be dead