NE555 — three bench projects

Reference setup

NE555P in PDIP8, isolated bench supply set to 5.00 V with current limiting. Use short connections, a multimeter and an oscilloscope with suitable probes. These are bench projects; none of their outputs controls a transmitter.

With CT of 10 µF, nominal frequency varies from 0.626 to 4.8 Hz. Replacing it with 1 µF gives 6.26 to 48 Hz. High duty cycle stays above 50% and varies with RV1. STOP holds RESET low.

Circuit schematic

Identical labels indicate the same electrical net even when a wire is not drawn between cells. Every terminal is identified. Capacitor + signs show polarity; NC marks an unconnected pin. The JSON netlist is the wiring reference.

Bill of materials

Pinout and layout

NE555 PDIP8, top view: 1 GND, 2 TRIG, 3 OUT, 4 RESET, 5 CONT, 6 THRES, 7 DISCH, 8 VCC. Check the notch, package and manufacturer pinout before insertion. Potentiometer terminal names describe their function, not a universal physical order.

Place CDEC close to pins 8 and 1, and CCONT close to pin 5. Keep TIMING and TRIGGER wiring short. Audio load returns must not share the sensitive input return path. No qualified PCB is supplied.

Assembly steps

1. With power off, identify sockets and check values. Keep ICs out of their sockets during continuity checks.
2. Wire J1, grounds and supply capacitors. Check for shorts and correct polarity.
3. Wire NE555 pins from the netlist, then CCONT and the timing network.
4. Join pins 2 and 6 at TIMING. RA connects V5 to DISCHARGE; RB and RV1 then lead to TIMING. Join potentiometer W and B.
5. Fit CT of 10 µF, positive to TIMING, then STOP and the LED. Keep the alternate 1 µF capacitor separate; it replaces CT rather than adding in parallel.
6. Check every net, switch power off, insert ICs with the correct orientation and prepare test points.

First power-up

1. Set 5.00 V and an initial 50 mA current limit. Power up; stop for persistent limiting, rapid heating or incorrect voltage. Connect probe grounds only to TP0/GND.
2. Observe TP2 and TP3 with a ×10 probe. After several cycles, measure period, high time and low time at both RV1 extremes.
3. Compare nominal calculations with measurements. TP2 moves approximately between V5/3 and 2 V5/3; OUT does not necessarily reach the positive rail. An LED cannot measure these levels.
4. Switch off, discharge CT and replace it with 1 µF. Repeat measurements; nominal frequency increases tenfold. Check STOP and record startup transients separately from steady operation.
5. Record levels, settings and instruments. These test points are for this dossier measurements, not an unknown input or a transmitter.

Troubleshooting

1. Excess current or heating: switch off and check rails, orientation, polarity and shorts before trying again.
2. No activity: verify the actual PDIP8 pinout, V5 and GND, then RESET, TRIG and THRES. Measure these before replacing the IC.
3. No oscillation: check RESET, the joined pins 2 and 6, the RA/RB/RV1 path and CT connection to GND.
4. Unexpected range: measure RV1 with power off, check wiper joined to B and verify CT value. Duty cycle variation is normal in this circuit.
5. Erratic behaviour: shorten wiring and check local decoupling, grounds and contacts. Sound or an LED cannot rule out parasitic oscillation.

Calculations and assumptions

RBtotal includes RB and the used part of RV1. The equations describe steady operation of the classic circuit, not 50% duty cycle. TP3 is not a 50 Ω source or a universal logic output.

tH ≈ 0.693 (RA + RBtotal) CT; tL ≈ 0.693 RBtotal CT

RA = 10 kΩ; RBtotal = 10…110 kΩ

CT = 10 µF → f ≈ 0.626…4.8 Hz; DH ≈ 52.2…66.7%

CT = 1 µF → f ≈ 6.26…48 Hz; DH unchanged

TP2 ≈ VCC/3…2 VCC/3; TP3: high-impedance measurement only

Nominal analytical values exclude full tolerances, capacitor leakage and device variation. A calculated range is not a manufacturer guarantee. Record actual measurements on the blank worksheet.

Measurement worksheet

Record supply voltage, current, fitted components, test points and waveforms. The supplied worksheet is blank and contains no prefilled results.

Supply and current

________________________________________

Frequency / duration / duty cycle

________________________________________

Output levels and load

________________________________________

Instruments, observations, decision

________________________________________

Dossier files

• Circuit schematic · SVG
• Netlist and design · JSON
• Calculations and assumptions · JSON
• Bill of materials · CSV
• Localized instructions · TXT
• Measurement worksheet · CSV

Manufacturer sources

• Texas Instruments NE555 — SLFS022K, March 2026

French source and agent-reviewed English pivot; other languages use machine translation with field and technical-token checks. No professional linguistic review is claimed. Schematics and netlists are shared across languages.