What does it do?
| The bulb subsystem converts the input signal into light. |
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How does it operate?
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Bulb circuit
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
The bulb is on when the signal coming into the driver providing the input signal is high. Otherwise, the bulb is off.
The bulb must be connected to a transistor, darlington or MOSFET driver subsystem.
Bulbs come in a variety of voltages and currents. The power supply for the bulb (which can be separate from the supply for the rest of the electronics) must provide the voltage needed by the bulb.
The driver providing the input signal must be able to provide a current considerably larger than the specified current for the bulb, because the current in the bulb is higher until the filament warms up (a safety margin of ´10 is advisable). |
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MES Bulb
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The bulb is connected between the supply rail (+Vs) and the input signal from the driver. This acts as a load on the driver.
When the input signal coming into the bulb subsystem is low, a potential difference across the bulb causes current to flow. It is this current that causes the bulb to light. |
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MES Bulb Holder
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Bulbs also come in a variety of sizes and fittings: T1, LES, MES and SBC. Probably the most common is MES (Miniature Edison Screw).
Bulbs need to be fitted into a corresponding style of holder to allow the electrical leads to be easily connected.
Some bulbs are available with leads attached. |
Possible applications
- Providing illumination
- Acting as an indicator or warning
Making
A PCB-mounting terminal block
Normally a bulb would not be mounted on the PCB. Usually a terminal block is mounted on the PCB and wires from this are connected to the bulb holder.
Build and test the unit that will provide the driving input signal before adding the bulb.
Testing
Make sure that the bulb switches on and off as power is applied from the driver unit.
Fault finding
If there is a fault, check the bulb by removing it from the circuit, placing it in a new holder and applying power to it directly. Check the voltage at the terminals of the terminal block. Check the resistance between the leads to the bulb holder (with the bulb inserted).
Alternatives
- LEDs are cheaper but they do not give as much light.
- Electro-luminescent displays can be used to produce more sophisticated visual displays but are more expensive.
- Low voltage halogen lighting can be controlled by electronics via a relay. It provides much brighter lighting than an ordinary filament bulb but is more expensive.
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