Instrument Droid

Goal

The main purpose of this lab is to design an intelligent measurement system, called an instrument droid. It is a custom instrument specifically designed to characterize any voltage source, or voltage regulator module (VRM) by measuring its Thevenin voltage and the Thevenin resistance as a function of output current. The Board is designed with all the best practices in reducing noise and Near Field Emissions.

Plan of Record

Features of the Board

1. I am using 4 layers PCB for easy routing without worrying about cross-under through ground plane. 4 layers stack up is made in such a way that Top and Bottom layer are both signal planes and middle two layers are ground planes.

2. At the input switch is added to get the input power either from the power jack or from the USB micro but not from both simultaneously.

3. TVS Diode is added for protection against ESD to the USB slot of the computer.

4. ICSP Pins are included for initial Boot loading of ATmega 328P.

5. A 16 MHz clock is used at ATmega 328.

6. CH340G is used for USB UART Communication. A 12 MHz clock is used at CH340G.

7. All IC inputs have decoupling/bypass capacitor.

8. Added a switch to set the max current between 300mA and 3A based on the selection of 1Ω and 10Ω sense resistors.

9. A switch is added to select VRM either from Power jack or from a screw terminal.

10. LEDs are added to indicate the power coming on the board.

11. ADC is used to read the differential voltage from sense resistor and VRM.

12. A DAC along with MOSFET and OP-Amp is used as a current source.

13. Smart LEDs and Buzzer are added as an indication of the start of the current.

Schematic

Layout

Assembled PCB

Measurement of Thevenin Resistance for different VRM

I have measured all possible waveforms on commercial Arduino and did a comparison of all waveforms with Golden Arduino to prove there is 20 to 50% noise reduction in Golden Arduino. Below is a detailed report for your reference.