ReferenceExaminable
Numbers to know
Every number the course expects you to have, in class order. It is generated from the classes themselves, so it cannot drift from what you were actually taught. There is a five minute verbal quiz at the top of every class.
Class 1 · What Electricity Does in a Theatre #
| Quantity | Value |
|---|---|
| Ohm's law | V = I × R |
| Power | P = V × I |
| Power in a resistance | P = I² × R |
| Mains voltage, Hong Kong and UK | 220–240 V RMS, 50 Hz |
| Mains voltage, North America | 120 V RMS, 60 Hz |
| Peak of a 230 V RMS sine | about 325 V |
| RMS to peak, sine wave | multiply by 1.414 |
| Three phase to single phase ratio | 1.73 (√3) |
| Phase to phase on a 220 V system | about 380 V |
| Current a 1 kW load draws at 230 V | about 4.3 A |
| Current a 1 kW load draws at 120 V | about 8.3 A |
| Typical domestic socket circuit | 13 A plug fuse, 20–32 A circuit breaker |
| Resistance of a good connection | under 0.1 Ω |
| Voltage dangerous to a person, AC | above 50 V RMS |
| Voltage dangerous to a person, DC | above 120 V |
Class 2 · Measure, Test, Prove #
| Quantity | Value |
|---|---|
| Typical multimeter input impedance, voltage mode | 10 MΩ |
| Typical multimeter resistance, current mode | under 1 Ω, plus the shunt |
| Continuity beep threshold, typical | under 30–50 Ω |
| Good cable conductor, end to end | under 1 Ω |
| Good connection, resistance | under 0.1 Ω |
| Suspect connection, resistance | above 0.5 Ω |
| Dry skin, hand to hand | 10 kΩ to 100 kΩ |
| Damp or broken skin, hand to hand | 1 kΩ or less |
| Average-responding meter error on non-sine | 20–40 per cent, direction unpredictable |
| Loading error becomes significant when source is | above about 100 kΩ |
| Proving procedure | live, dead, live |
| Fresh alkaline AA cell | 1.5–1.6 V |
| Alkaline AA considered flat | below 1.1 V under load |
| Meter fuse, typical current range | 200 mA fast blow, and 10 A |
Class 3 · Components and Connectors #
| Quantity | Value |
|---|---|
| Silicon diode forward drop | about 0.7 V |
| Schottky diode forward drop | about 0.3 V |
| Red LED forward voltage | 1.8–2.2 V |
| Green or blue LED forward voltage | 3.0–3.4 V |
| Typical indicator LED current | 10–20 mA |
| LED series resistor formula | R = (V_supply − V_f) ÷ I |
| RC time constant | τ = R × C |
| Charge reached in one time constant | 63 per cent |
| Time constants to be fully charged | 5 |
| Standard resistor tolerance, gold band | ±5 per cent |
| Standard resistor tolerance, brown band | ±1 per cent |
SMD marking 472 | 4.7 kΩ |
| Common decoupling capacitor | 100 nF, at each chip |
| Relay coil flyback spike, unprotected | hundreds of volts |
| DMX connector | 5-pin XLR |
| Balanced audio connector | 3-pin XLR |
| Mains connector, locking | powerCON or TRUE1 |
| Socapex circuits per cable | 6 |
Class 4 · Soldering and Fabrication #
| Quantity | Value |
|---|---|
| Iron temperature, leaded solder | 340–370 °C |
| Iron temperature, lead-free | 370–400 °C |
| Leaded eutectic solder melting point | 183 °C |
| Lead-free (SAC305) melting point | 217–220 °C |
| Time on a typical joint | 2–4 seconds |
| Jacket strip length for XLR | about 25 mm |
| Maximum untwist at an RJ45 | 13 mm |
| Minimum cable bend radius | 8 × cable diameter |
| XLR pin 1 | Screen |
| XLR pin 2 | Hot, positive |
| XLR pin 3 | Cold, negative |
| DMX 5-pin, pin 2 | Data minus |
| DMX 5-pin, pin 3 | Data plus |
| DMX cable impedance | 110 Ω |
| T568B first pair | orange-white, orange |
| RJ45 pair on pins 3 and 6 | green-white, green |
| Acceptable joint resistance | under 0.05 Ω |
Class 5 · Loads, Switching and Isolation #
| Quantity | Value |
|---|---|
| Microcontroller pin current, safe maximum | about 20 mA |
| Relay operate time | 5–15 ms |
| Relay coil flyback spike, unprotected | hundreds of volts |
| Relay life, mechanical | tens of millions of operations |
| Relay DC derating from its AC rating | often 20:1 or worse |
| Logic-level MOSFET gate threshold | 1–2 V, fully on by 4.5 V |
| Standard MOSFET gate threshold | 2–4 V, needs 10 V to be fully on |
| Typical power MOSFET R_DS(on) | 10–50 mΩ |
| MOSFET dissipation | P = I² × R_DS(on) |
| Optocoupler isolation voltage | 2.5–5 kV |
| SSR forward drop while conducting | 1–1.5 V |
| Tungsten lamp inrush | 10–15 × running current |
| Switch-mode supply inrush | 20–100 A, 1–10 ms |
| Motor starting current | 5–8 × running current |
| Recommended sequencing interval | about 1 second between groups |
Class 6 · Build a Driver Board #
| Quantity | Value |
|---|---|
| Optocoupler LED series resistor, 5 V logic | 220 Ω |
| MOSFET gate series resistor | 100–220 Ω |
| Input and gate pull-down | 10 kΩ |
| Indicator LED resistor, 12 V | 1 kΩ |
| IRLZ44N R_DS(on) | about 22 mΩ |
| IRLZ44N gate threshold | 1–2 V |
| PC817 isolation voltage | 5 kV |
| Board quiescent current, all channels off | a few mA |
| Expected supply-terminal resistance, dead test | tens of kΩ, rising |
| Expected control-to-load ground resistance | open circuit |
| Expected gate-to-source resistance | about 10 kΩ |
| Insulation test voltage | 500 V |
| Dissipation at 5 A through 22 mΩ | about 0.55 W |
| Documented failure mode on signal loss | outputs off |
Class 7 · Analogue Signal, Impedance and Grounding #
| Quantity | Value |
|---|---|
| Microphone level | 1–50 mV |
| Consumer line level | −10 dBV, about 0.316 V |
| Professional line level | +4 dBu, about 1.23 V |
| dBu reference | 0.775 V |
| dBV reference | 1 V |
| Voltage ratio for 6 dB | 2 |
| Voltage ratio for 20 dB | 10 |
| Impedance bridging ratio | load at least 10 × source |
| Microphone source impedance | 150–600 Ω |
| Microphone preamp input impedance | 1.5–3 kΩ |
| Line input impedance | 10 kΩ or more |
| DI box instrument input impedance | about 1 MΩ |
| Typical audio cable capacitance | about 100 pF per metre |
| Good balanced input CMRR | 60–90 dB |
| Mains hum fundamental | 50 Hz, or 60 Hz |
| Chassis-to-chassis potential in a loop | a few mV to a few hundred mV |
| XLR screen lift | disconnect pin 1 at the receiving end |
Class 8 · Hum Hunting and Scope Work #
| Quantity | Value |
|---|---|
| Mains hum fundamental | 50 Hz or 60 Hz |
| Rectifier ripple frequency | 100 Hz or 120 Hz |
| Switch-mode supply switching frequency | 20 kHz to several hundred kHz |
| Scope probe attenuation, ×10 setting | divide by 10 |
| Period of 50 Hz | 20 ms |
| Period of 1 kHz | 1 ms |
| Period of 100 Hz | 10 ms |
| Frequency from period | f = 1 ÷ T |
| Acceptable ripple on a 12 V rail | under about 100 mV peak to peak |
| Scope ground clip potential | mains earth, always |
| Half-split searches for 16 items | 4 tests |
| Sequential search for 16 items | up to 16 tests |
| Peak of 230 V RMS | about 325 V |
| Typical hum level worth chasing | anything above −60 dB relative to programme |
Class 9 · Data, Protocols and Networks #
| Quantity | Value |
|---|---|
| DMX512 bit rate | 250 kbit/s |
| DMX bit duration | 4 µs |
| DMX slot duration, with framing | 44 µs |
| DMX break, minimum | 92 µs |
| Mark after break, minimum | 12 µs |
| DMX start code, normal data | 0x00 |
| Slots in one universe | 512 |
| Full universe packet time | about 22.7 ms |
| Full universe refresh rate | about 44 Hz |
| DMX cable impedance | 110 Ω |
| DMX terminator | 120 Ω across the data pair |
| Maximum devices per DMX run | 32 |
| Maximum DMX run length | about 300 m |
| DMX connector | 5-pin XLR |
| MIDI bit rate | 31.25 kbit/s |
| sACN transport | UDP multicast |
| Art-Net transport | UDP, commonly broadcast |
| Signal velocity in copper cable | about two thirds the speed of light |
Class 10 · Build and Break a Rig #
| Quantity | Value |
|---|---|
| Maximum devices on one DMX run | 32 |
| Maximum DMX run length | about 300 m |
| DMX terminator | 120 Ω |
| Universes carried by one Cat5e cable | many, limited by bandwidth not connectors |
| Channels in a universe | 512 |
| sACN default transport | UDP multicast |
| Art-Net default transport | UDP broadcast |
| Common Art-Net address range | 2.x.x.x or 10.x.x.x |
| Link speed indicating a damaged pair | 100 Mbit/s where 1 Gbit/s is expected |
| Half-split tests for 16 devices | 4 |
| Time to find a fault with a correct drawing | typically under 2 minutes |
| Time to find the same fault without one | typically 10 minutes or more |
| Devices per active splitter output | up to 32, per output |
Class 11 · Microcontrollers #
| Quantity | Value |
|---|---|
| Microcontroller pin current, safe maximum | about 20 mA |
| Typical pull-up or pull-down resistor | 10 kΩ |
| 10-bit ADC range | 0–1023 |
| 12-bit ADC range | 0–4095 |
| 10-bit ADC step with a 5 V reference | 4.9 mV |
| Maximum recommended ADC source impedance | about 10 kΩ |
| Switch bounce duration | 1–20 ms |
| Typical software debounce time | 20–50 ms |
millis() overflow period | about 49 days |
| PWM frequency, visible flicker below | about 100 Hz |
| PWM frequency, audible whine band | 200 Hz – 20 kHz |
| PWM frequency for broadcast-safe lighting | above about 20 kHz |
| ATmega328 clock speed | 16 MHz |
| Duty cycle for half power | 50 per cent, but not half perceived brightness |
Class 12 · Program a Prop #
| Quantity | Value |
|---|---|
| Power-up state, always | the safe one, outputs off |
| DMX loss detection window | about 1 second with no valid packet |
| Typical debounce time | 20–50 ms |
| Watchdog timeout, typical | 1–2 seconds |
| Reset action | one deliberate physical action, 2 second hold |
| Status indicator, idle | one blink |
| Status indicator, fault | rapid blinking |
| RS-485 receiver for DMX | MAX485 or equivalent, isolated |
| PWM frequency for a stage lamp | above 20 kHz if cameras are present |
| Sensor reading outside its physical range | treat as a fault, go to SAFE |
| Loop pass time, target | under 1 ms |
| Documentation sheet | one side of A4, in the case |
Class 13 · Sensors and Actuators #
| Quantity | Value |
|---|---|
| Voltage divider | V_out = V_in × R2 ÷ (R1 + R2) |
| Divider fixed resistor, rule of thumb | geometric mean of the sensor's range |
| Maximum ADC source impedance | about 10 kΩ |
| LDR range, bright to dark | about 1 kΩ to 100 kΩ |
| Typical solenoid duty cycle rating | 25 per cent unless stated otherwise |
| Peak and hold, holding duty | typically 30–50 per cent |
| Hobby servo control pulse | 1.0–2.0 ms, repeated every 20 ms |
| Common stepper step angle | 1.8 degrees, so 200 steps per revolution |
| Quadrature encoder counts per detent | 4 edges |
| Debounce time, typical | 20–50 ms |
| Relay actuation delay | 5–15 ms |
| Ultrasonic sensor useful range | about 2 cm to 4 m |
| Safety contact wiring | normally closed, so a break reads as unsafe |
| Incremental encoder at power-up | position unknown, must be homed |
Class 14 · Build a Triggered Effect #
| Quantity | Value |
|---|---|
| Chain latency for a tightly timed effect | under about 50 ms |
| Debounce contribution to latency | 20–50 ms |
| Network hop contribution | 5–50 ms |
| Relay actuation | 5–15 ms |
| Cycle test, minimum | 100 operations |
| Thermal test duration | 15 minutes at worst realistic duty |
| Interruption test | power cut at 3 different points in the cycle |
| Component temperature needing an explanation | anything you cannot hold a finger on |
| Documentation | one side of A4, in the case |
| Handover test | a stranger operates it from the sheet alone |
| Trigger patterns | cue arms and sensor fires; either fires; both within a window |
| Power-up state | safe, outputs off, every time |
Class 15 · Safety Systems and Fault-Finding #
| Quantity | Value |
|---|---|
| Perception threshold, 50 Hz AC | 0.5–2 mA |
| Let-go threshold | about 10 mA |
| RCD trip threshold, personal protection | 30 mA |
| RCD trip time | under 30 ms |
| Current likely to cause fibrillation | 50–100 mA |
| Body resistance, dry skin, hand to hand | 10 kΩ – 100 kΩ |
| Body resistance, damp or broken skin | 1 kΩ or less |
| Current at 230 V through 1 kΩ | 230 mA |
| Safe touch voltage, AC | below 50 V RMS |
| Safe touch voltage, DC | below 120 V |
| Typical plug fuse | 13 A, protecting the cable |
| Emergency stop wiring | normally closed, latching, dual channel, monitored |
| Locks required for isolation | one per person working |
| Proving procedure | live, dead, live |
| Half-split tests for 16 points | 4 |
| Escalate after | 30 minutes with no boundary established |
Class 16 · Capstone and Fault-Finding Exam #
| Quantity | Value |
|---|---|
| Capstone weighting, the build | 25 per cent |
| Capstone weighting, the proof | 25 per cent |
| Capstone weighting, the documentation | 20 per cent |
| Capstone weighting, the fault exam | 30 per cent |
| Fault exam, systems | 3 |
| Fault exam, time per system | 30 minutes |
| Documentation length | one side of A4 |
| Documentation points required | 10 |
| Look-do-not-touch phase | first 5 minutes |
| Escalate after | 30 minutes with no boundary established |
| Response to a safety issue in the exam | stop, isolate, report |
| Marks for a logged partial diagnosis | above an unlogged lucky find |