Lab 0.1 — Power Supply + Fluke Safety

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Goal

Before a single component is powered, learn to operate the two instruments that everything else depends on: the WANPTEK bench power supply and the Fluke 117 multimeter. Specifically, learn to set a current limit that protects your circuit, and to use the DMM without blowing its fuse or your parts. This is the single most important habit in the whole course — a correctly set current limit is the difference between a wiring mistake that does nothing and one that releases smoke. If you internalize constant-voltage vs. constant-current here, every later lab is safer.

Recommended reading

• Kuo Ch. 1 — the real-time DSP system context (why we care about clean, well-characterized supplies feeding converters). Light read.
• Your instruments’ manuals: the WANPTEK quick-start (CV/CC, OCP) and the Fluke 117 manual (input jacks, fuse ratings, VoltAlert). Read the jack/fuse section in full.
• PEI Ch. 7 — Hands-on Electronics: multimeters, power supplies, breadboards, and safe measurement practices at reference depth. Skip the soldering, PCB-fabrication, and specialized-tools sections until needed.
• No Course 1 dependency — this is pure bench skill.

Equipment & parts

• WANPTEK 30 V / 10 A DC bench power supply + its output leads.
• Fluke 117 DMM + test leads.
• One resistor from the kit: 100 Ω (and optionally a 1 kΩ), ¼ W.
• Breadboard + a couple of jumper wires (used only as a load holder).

Wiring & bench setup

The chain: the WANPTEK sources a current-limited 5 V, the 100 Ω resistor on the breadboard is the load, and the Fluke sits in series in the − return for the current parts (C–D) — or in parallel across the output for the voltage part (B).

flowchart LR
  PSU["WANPTEK 30V/10A<br/>5.0 V set, limit ~100 mA"]
  R["100 Ω ¼ W<br/>breadboard load"]
  DMMA["Fluke 117<br/>dial DC amps, red in A jack<br/>(Parts C–D, in series)"]
  DMMV["Fluke 117<br/>dial DC volts, red in VΩ<br/>(Part B, in parallel)"]
  PSU -- "+ output" --> R
  R -- "return through meter" --> DMMA
  DMMA -- "COM → − output" --> PSU
  PSU -. "across + / −" .-> DMMV

flowchart LR
  PSU["WANPTEK 30V/10A<br/>5.0 V set, limit ~100 mA"]
  R["100 Ω ¼ W<br/>breadboard load"]
  DMMA["Fluke 117<br/>dial DC amps, red in A jack<br/>(Parts C–D, in series)"]
  DMMV["Fluke 117<br/>dial DC volts, red in VΩ<br/>(Part B, in parallel)"]
  PSU -- "+ output" --> R
  R -- "return through meter" --> DMMA
  DMMA -- "COM → − output" --> PSU
  PSU -. "across + / −" .-> DMMV

Pin map (every wire; Fluke jack per part of the procedure):

From	To	Fluke jack / lead
WANPTEK + output	100 Ω leg 1 (e.g. breadboard column 10)	— (supply’s own red lead + jumper)
100 Ω leg 2 (column 12)	Fluke red probe	red lead in the A jack, dial A⎓ (Parts C–D only)
Fluke black probe	WANPTEK − output	black lead in COM (all parts)
Part B only: Fluke red probe	WANPTEK + output (no resistor in the path)	red lead in VΩ, dial V⎓

     WANPTEK PSU              breadboard (load holder only — rails unpowered)
    ┌────────────┐        ┌──────────────────────────────────┐
    │   +   ●────┼────────┤ col10 ●──[ 100 Ω ]──● col12      │
    │            │        └──────────────────────┬───────────┘
    │            │                               │ jumper
    │            │            Fluke 117          │
    │            │       ┌─────────────────┐     │
    │   −   ●────┼───────┤ COM         A ● ├─────┘
    └────────────┘ black └─────────────────┘ red (A jack, dial A⎓)

Setup gotchas: the resistor’s two legs must land in two different columns (both legs in one 5-hole column = the resistor is shorted by the breadboard itself). Leave the − return open until the meter is inserted — the meter is that wire in Parts C–D. The breadboard carries no power in this lab (no MB102 module needed). After Parts C–D, move the red lead back to VΩ before you put the meter away.

Safety & don’t-break-it

• The Fluke’s A (current) jack is a near-short. With a lead in the A jack and the dial in current mode, the meter is ~0 Ω. If you touch those leads across the supply output you create a dead short. The supply’s current limit (set below) is what saves you, but the correct habit is: leads live in the V/Ω/COM jacks; only move to A deliberately, in series, and move back immediately after.
• Never connect the DMM in current mode in parallel with a source or component. Current is always measured in series (the meter becomes part of the loop).
• Set the current limit before connecting a load (procedure below). Treat “I forgot to set the limit” as a stop-and-restart event.
• The 100 Ω resistor across a supply dissipates real power — at 5 V it sinks 50 mA and dissipates 0.25 W, right at a ¼ W part’s rating. Don’t leave it energized at higher voltages; it will get hot.
• Keep one hand away from the circuit when powered; never let the two output leads touch.

Background

A bench supply has two regulation modes. In constant-voltage (CV) it holds the set voltage and delivers whatever current the load draws, up to a ceiling. When the load tries to draw more than the current limit \(I_\text{lim}\) you set, the supply switches to constant-current (CC): it holds the current at \(I_\text{lim}\) and drops the voltage as far as needed. A dead short in CC mode simply sits at \(I_\text{lim}\) with the output near 0 V — safe.

For a resistor \(R\) across a CV supply at voltage \(V\), Ohm’s law predicts the current and power:

\[I = \frac{V}{R}, \qquad P = VI = \frac{V^2}{R}.\]

For \(V = 5\text{ V}\), \(R = 100\ \Omega\): \(I = 50\text{ mA}\), \(P = 0.25\text{ W}\). If your set current limit is above 50 mA the supply stays in CV; set it below 50 mA and you’ll watch it drop into CC — a deliberate, instructive demonstration.

Procedure

Part A — Set a current limit (do this every session).

1. Power on the WANPTEK with nothing connected to the outputs.
2. Set the voltage knob to 5.0 V (read it on the display).
3. Set the current limit: turn the current knob fully down, then briefly short the output leads together (or use the supply’s built-in method) — the display drops toward 0 V and the CC/constant-current indicator lights. Now dial the current up to ~100 mA. Remove the short. The supply now enforces a 100 mA ceiling.
4. Confirm: with the short removed, the display should read 5.0 V and 0.00 A (CV, no load).

Part B — Measure the supply voltage with the Fluke.

5. Put the Fluke leads in COM (black) and VΩ (red). Turn the dial to V⎓ (DC volts).
6. Touch red to the supply’s + output, black to −. Read ≈ 5.00 V. This confirms both the supply and your DMM voltage function.

Part C — Constant-voltage: measure load current in series.

7. Power off the supply output. Build a one-resistor circuit (per Wiring & bench setup): supply + → one leg of the 100 Ω resistor; other leg → back toward supply −, but leave the − return open where the meter will go.
8. Move the Fluke’s red lead to the A jack and set the dial to A (DC current). Insert the meter in series in that open return: supply − → meter COM, meter A → resistor.
9. Power on. The Fluke should read ≈ 50 mA; the supply should stay in CV at 5.0 V and show ≈ 0.05 A. The two current readings should agree.
10. Power off. Move the red lead back to VΩ and the dial back to volts.

Part D — Force constant-current (see the limit work).

11. Re-set the supply current limit to ~20 mA (Part A method).
12. Power on the same 100 Ω circuit. The load wants 50 mA but the supply caps it: it enters CC, the CC indicator lights, current holds at ~20 mA, and the voltage sags to \(V = I_\text{lim} R \approx 0.02 \times 100 = 2\text{ V}\).
13. Confirm with the Fluke (voltage across the resistor ≈ 2 V). Power off.

Deliverable & expected results

Where results go (pure-instrument lab — no firmware or host code; the bench note is the whole artifact):

Artifact	Path
Bench note (readings below + the CV/CC story)	labs/lab-0-1/notes.md

A short bench note (labs/lab-0-1/notes.md) recording:

• The CV reading: 5.00 V, 50 mA, supply in CV.
• The CC reading: current pinned at your limit (~20 mA), voltage sagged to ≈ 2 V, supply in CC.
• A one-line statement of why the voltage sagged (the supply gave up voltage to hold current).

Quantity	Predicted	Measured
Load current (CV, 5 V, 100 Ω)	50 mA	…
Power in resistor	0.25 W	…
Voltage in CC at 20 mA	2.0 V	…

Analysis & reconciliation

Compute \(I = V/R\) and \(P = V^2/R\) by hand and compare to the meter. Expect small discrepancies (a few %): the resistor’s tolerance (often ±5%), the meter’s burden voltage in current mode (the meter’s own small resistance drops a little voltage in series), and the supply’s set-point accuracy. If your CC voltage isn’t exactly \(I_\text{lim}R\), check whether the resistor’s true value (measure it in Lab 0.2) explains it.

Going further

• Repeat Part C with a 1 kΩ resistor and predict the current first (5 mA). Notice the meter’s burden voltage matters even less at lower currents.
• Explore the supply’s OCP (over-current protection) trip vs. simple CC foldback, if your unit distinguishes them.
• Read the Fluke’s capacitance and VoltAlert (non-contact) functions in the manual now; you’ll use capacitance in Lab 0.3.