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Astable multivibrator (alternating blinker)
A classic for beginners: two BC547 transistors make two LEDs blink alternately. With 47 kΩ and 10 µF they switch about every 0.3 seconds; runs on 5 to 9 V. Single-sided, no wire jumper.
- Size
- 76 × 56 mm, 1.6 mm thick
- Material
- Circuit board (FR4)
- Difficulty
- Intermediate
- Milling time
- approx. 23 min
- Bits
- Engraving bit 30°, PCB drill Ø 0.8 mm, PCB drill Ø 1.3 mm, Corn cob router bit Ø 2 mm
- Customise
- Fixed template, freely editable once opened
Free with an account · carve with Chrome or Edge · no installation
Build instructions
Parts
| Qty | Part | Value | In layout |
|---|---|---|---|
| 2 | Resistor 0.25 W | 470 Ω Colour bands: yellow, violet, brown, gold | R1, R4 |
| 2 | Resistor 0.25 W | 47 kΩ Colour bands: yellow, violet, orange, gold | R2, R3 |
| 2 | Electrolytic capacitor Polarised: the stripe on the case is minus, the long lead is plus (square pad). | 10 µF / 16 V | C1, C2 |
| 2 | LED 5 mm The long lead is the anode; the flat side (cathode) points to the mark in the layout. | red | LED1, LED2 |
| 2 | NPN transistor Insert with the flat side as in the layout; do not swap the leads. | BC547 | T1, T2 |
| 1 | Screw terminal 2-pin, 5.08 mm pitch | X1 |
You also need: soldering iron (about 30 W, fine tip), 0.5 to 1 mm solder with flux, side cutters and a multimeter.
Assembly
- Mill the board: isolate the copper first, then drill, and finally mill out the holes and the outline. The order is shown in the Milling panel.
- Cut through the holding tabs, deburr the edges and rub the copper bright with a scouring pad. After that, do not touch the copper side with your fingers.
- Use a magnifier and a continuity tester to look for leftover copper between neighbouring traces; cut any bridges with a craft knife.
- Insert the parts from the side without copper and solder them on the copper side. Fit low parts first: resistors and diodes, then sockets and transistors, and finally capacitors, terminals and large parts.
- Before soldering, compare the polarity with the component layout: band of the diodes, flat side of the LEDs, minus stripe of the electrolytic capacitors, notch of the ICs.
- Solder each lead for about two seconds at around 330 °C: tip on pad and lead, feed solder until it flows all round. Then clip the leads just above the joint.
- Fit the transistors T1 and T2 with the flat side as in the layout; the leads are collector, base and emitter.
- The electrolytic capacitors C1 and C2 are cross-coupled: plus (long lead, square pad) points to the collector, i.e. towards the LED side.
- Visual check: no solder bridges, no dull, balled-up joints. Remove flux residue with isopropyl alcohol and an old toothbrush.
Test and power up
- Before switching on for the first time, check with the meter that there is no short between plus and minus of the supply. Power up the first time on a bench supply with current limiting if possible.
- Apply 5 to 9 V to X1: the LEDs alternate about every 0.3 seconds.
- If only one LED stays lit, check the polarity of the capacitors and the orientation of the transistors.
- Finally protect the copper side against oxidation with solder lacquer or plastic spray.
How to carve this template
- OpenOpen the template in the app and adjust size and text if you like.
- CheckLook at it in 3D, check run time and warnings.
- Set upThe carve wizard guides you through material, clamping, bit and zero point.
- CarvePress start; the app drives your Grbl router directly over USB.
