Stanford summer project

Summer Internship ProjectNikhil Ghosh (Gunn High School)May - August, 2014Kasevich Lab, Stanford University

Internship Goals

To acquire fluency in KiCAD, circuit design, and electrical engineering concepts

To build a board which can be used to protect the lab’s “slow analog out” board, therefore protecting the apparatus and setups from damage

Premise and Background

All channels of slow board are set to different voltages, as they all serve different purposes

Voltages of each channel are manipulated and preset by the computer

Main Problem and Desired OutcomeThe 10V Crisis:When the board is turned off and on again (e.g. in a power outage), all of its channels are reset to 10V. This overrides the computer’s preset voltages for each channel, and is dangerous for the connected instruments

When the voltage is reset, all channels should be broken to avoid potential damage to instruments

Initial Focus

To design a board and install a switch, which can make or break the channels’ connections depending on its comparative analysis of the current voltage, using:

1. Analog switches2. Comparators3. Timer/Delay systems

Stage 1: Brainstorming and Planning

After pondering the problem and researching methods available to avert “The 10V Crisis”, I designed a basic layout for what the solution board would look like...

Solution: Black Box Diagram of Board

Stage 2: Component Selection

By studying the specs of the Analog Board and a multitude of parts found online, I narrowed the field of types of usable components

Solution: Detailed Black-Box Diagram

Stage 3 Stage 4DigiKey and several other online catalogues were used to select specific components which met our requirements. These included analog switches, NOR gates, and window comparators

KiCAD was used in order to create a schematic for this project. The project is now going through the final development stages of KiCAD’s process (i.e. PCB layout, etc)

General Step by Step Solution1. Comparator and switch break the channels (at 10V)2. Computer resets channels 39-2 to ideal voltages3. Then, computer sets Channel 1’s voltage to one within the frame of the window comparator, which gives out 5V (Logic 1)4. This sets forth the action to close the switch, but it is delayed by the RC delay circuit5. While the switch is closing, the computer sets Channel 1’s voltage to that needed by the device connected to Channel 16. The switch closes, and all channels are running at their ideal voltages

Details of the Solution (Parts, etc)

Significant ComponentsWindow Comparator: Compares a given voltage to a preset and adjustable frame of reference. Based on this comparison, it outputs Logic zero or one (0V/5V)

The LM-393

Significant Components Cont’dNOR Gate: This is a type of logic gate, and it only allows the first set voltage (to Channel 0) to influence the switch

RC Circuit: Delays the current so that the computer has time to reset Channel 0’s voltage (again) before the switch fully closes

Additional PartsDiode clamps, voltage regulators, and filter capacitors to protect the components and to pare down signal noise

SMA connector plugged into logic output so that coaxial cables can also be connected (not just ribbon wires)

Trimpots (adjustable resistors) make it possible to customize the window of voltage reference

Additional Parts Cont’dLED connected to logic output as well, using minimum current (on/off = logic 1/0)

+ Monitor status visually+ Assist in debugging (voltage flow)

Challenges and Interesting BitsUnderstanding error messages in KiCAD and knowing when to disregard them

Importing and creating footprints/components and understanding how to manage KiCAD’s libraries

Controlling the board through one of the channels, eliminating the need for any additional external wiring

Lessons Learned - KiCAD proficiency, and basic circuit design- Basic understanding of electrical rules and concepts- Troubleshooting in KiCAD- Footprint design and implementation- Strategic circuit-oriented problem solving- Familiarity with spec sheets, properties of components

AcknowledgementsJason HoganChristine DonnellyAlex SugarbakerSusannah Dickerson Tim Kovachy Chris Overstreet Raj KrishnakumarMark Kasevich

Thanks to all of these people for their support and for giving me this amazing opportunity to learn so much.

This exposure has opened my eyes to a huge number of fields and I am extremely grateful.