Ultra-Lite Digital SMU
Part 2 - Hardware Prototype using an Arduino
Let's build an ultra-lite SMU to learn digital control. Why? A small system provides an easy on-ramp to grasp bigger
ideas without getting lost in a myriad of circuit details. Later,
you can develop more complex SMU's on a solid foundation.
Part 1 - describes the essential
blocks of a digital SMU (with SPICE file).
Part 2 - builds a prototype with the Arduino and a just few components.
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SMU SPECIFICATIONS
- Force Voltage: 0 to +4V
- Force Current: 0 to +5mA
- Current Sense
- Resistor: Rs = 100 ohms
- Voltage: Vs = 5mA*100 ohms = 0.5V max
SCHEMATIC
Here's the schematic of our SMU showing connections between the Solderless Breadboard, a DAC board and the Arduino UNO Board.
CIRCUIT NOTES
- The block diagram above shows 2 ADCs. However, the Arduino achieves a similar function with a single DAC and switches for inputs A0 and A1.
- An external DAC board acheives and higher resolution and faster response than the Arduinos PWM output.
- Each analog input (A0,A1) has an RC low-pass filter to reduce noise and provide a low-Z source to drive the ADC's Sample and Hold capacitor.
PROTOTYPE
There is no easier way to prototype a circuit than with the Solderless
Protoboards. Drop in a component and begin wiring! Although the breadboard
is limited to lower frequency designs, you can easily test, modify and
experiment with your design.
A handy online drawing program
(www.cirkitstudio.com/) allows you to create a parts-based wiring diagram as
shown below.
Please note, the diagram above is only a suggestion. Arrange parts and wire the circuit anyway you prefer!
PARTS LIST
Even with the most basic components, you can build a working SMU. Feel free to select alternate components for preference / availability / cost.
Qty
(Ref)Description Part Number
(Digikey option)1 Arduino Uno Rev3 Microcontroller Board A000066 1 USB Cable Type A/B generic 1 Solderless Breadboard, SparkFun Electronics PRT-12002 (1568-PRT-12002-ND) 1 pkg Jumper Wires, Various Lengths, M to M, Adafruit Industries (1528-2185-ND) 2
(R1,R2)RES 100K OHM ≤5% any available 1
(C1,C2)CAP CER 0.10UF X7R any available 5
(Rs)RES 100,1K,10k,100k,1M OHM ≤1%
(Various values for different ranges)any available
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