Interactive electronics resource
Transistor Flasher SMD Trainer Instructions
Build, understand and experiment with the Transistor Flasher SMD Trainer. This resource brings the original kit material into the current MitchElectronics format with the schematic, circuit explanation, component and PCB information, construction guidance, troubleshooting and practical ideas where available.
Introduction
What is the Transistor Flasher SMD Trainer?
The Transistor Flasher SMD Trainer kit is designed to test your skills at SMD soldering and provides you with a small circuit that blinks two different LEDs. The frequency of the blink is determined by the value of the electrolytic capacitors and the charging resistors, meaning that the rate of blinking is fixed. To learn more about the transistor flasher and how it works, you can check out the instructions for the Transistor Flasher kit from MitchElectronics which also includes the internal circuit diagram of the 555 itself.
What can you do with the Transistor Flasher SMD Trainer?
Besides the obvious use of improving your skills with soldering SMD parts, there are numerous uses for the kit. One potential application is to use the flashing LED as a night locator that can be attached to the back of a bag. Simply put, these kits can be ideal for quickly locating others at night during hikes in a similar fashion to tail and wing lights on planes.
On that note, the Transistor Flasher SMD Trainer can also be used on model RC planes that want to replicate the blinking lights used to locate craft at night. The SMD LEDs, albeit small, are brighter than you’d think, and can thus be used as a visual aid at a great distance during the night.
The Transistor Flasher kit is also excellent for pulsing circuits that need to turn something on and off at regular intervals. One such example is a clock source for digital logic circuits that need a regular pulsing voltage (however, if using the transistor flasher with logic circuits, make sure the logic circuit operates at the same voltage as the transistor flasher otherwise you will likely damage the logic circuit).
Schematic
Try it yourself
Circuit simulation
What you need
Component List
| Component | Quantity | PCB Reference |
|---|---|---|
| MMBT3904 Transistor | 2 | Q1, Q2 |
| 100µF Capacitor | 2 | C1, C2 |
| 680R Resistor | 2 | R1, R4 |
| 5.6K Resistor | 2 | R2. R3 |
| Red LED | 2 | D1, D2 |
| PP3 Connector | 1 | BT1 |
| Transistor Flasher SMD PCB | 1 | — |
Inspect the board
Interactive BOM
Board reference
PCB & assembly
The PCB silkscreen and component references should be checked against the component list before soldering each part.
Before applying power
- Check every component against its PCB reference.
- Confirm the orientation of all polarised components and ICs.
- Inspect for solder bridges, unsoldered pads and clipped leads that could cause a short.
- Check that no loose wire or solder debris remains on the board.
Build with confidence
Construction tips
Recommended build approach
Transistor Flasher SMD Trainer uses surface-mount components, so work methodically and inspect each joint as you go.
- Check the component values and package markings before soldering.
- Start with the smallest passive components and work towards larger devices and connectors.
- For multi-pin devices, align the package carefully and tack one pad first; correct the alignment before soldering the remaining pins.
- Use only enough solder to form a clean joint and watch closely for bridges between adjacent pads.
- Observe the orientation marks on diodes, LEDs, ICs and any other polarised components.
- Inspect the board under good light or magnification before applying power.
SMD soldering guidance
If you are new to surface-mount assembly, use the SMD Soldering Guide alongside these instructions. Keeping the tip clean, using flux where appropriate and checking alignment frequently makes the build much easier.
When it does not work
Troubleshooting
Nothing happens when power is applied
- Confirm the supply is connected to the correct input and with the correct polarity.
- Check that ICs, diodes, LEDs, transistors and electrolytic capacitors are fitted in the correct orientation.
- Compare component values and positions against the component list and PCB reference.
- Inspect for missed joints, dry joints and accidental solder bridges.
- Closely inspect fine-pitch and adjacent SMD pads for solder bridges or unsoldered ends.
The circuit powers up but does not behave as expected
This kit is intended for smd transistor flasher trainer. If the output is stuck, unstable or outside the expected behaviour, use the schematic to trace the circuit a stage at a time rather than replacing several parts at once.
Check the components around the part of the circuit responsible for the output or timing first. A misplaced resistor, reversed semiconductor or poor connection can allow a circuit to power up while preventing it from operating correctly.
The circuit works intermittently
Intermittent behaviour is often caused by a marginal solder joint, a loose connector or a component lead that has not been fully soldered. Gently inspect the board with power removed and reflow any joint that looks dull, cracked or incomplete.
If the fault remains, compare the assembled board with the schematic and PCB reference one connection at a time.
Ready to test and experiment?
To help keep the board stable when soldering, you can download a free STL model of a basic jig that can be 3D printed with all common 3D printers. Watch out for the mounting hole pins as they may be vulnerable to snapping if using a low infill density, low wall thickness, or thick layer heights. Additionally, do not use hot air to solder the PCB when using the jig as you will melt the jig. Coming Soon...
Once the board is working, compare its behaviour with the schematic and the explanation above. Try changing only one input, control or permitted component value at a time so you can clearly see what effect that change has on the circuit.