This audible electronic spirit level circuit is extremely valuable for folks with hearing or vision imperfections. Not only that, but it is also useful for people who wish to align everyday stuff without needing an accomplice.
The design of this circuit is fairly straightforward. The main element in the schematic is an optocoupler which equips an air gap that is relatively wide and will hold a small bubble level vial measuring around 30 x 10 x10 mm.
The LED in the optocoupler delivers infrared light which travels through the vial and later arrives at the opto-transistor. An LED and a transistor with a self-oscillation buzzer are linked parallelly to the first transistor.
When the IR light goes through the liquid, the transistor absorbs adequate light so that it can conduct. After that, the LED and buzzer will be inactive.
Once the air bubble is in the middle, the IR-light will be scattered just enough causing the opto-transistor to switch off. Due to that, the LED turns on and the buzzer will make noise.
The power supply for the circuit is delivered by a 5-V voltage regulator. Because the circuit will only be occasionally used and consumes lower than 100 mA, it can be effortless powered from a 9-V battery. LED2 functions as a power supply indicator to signify that the circuit is powered up and as a reminder, the circuit must be switched off after use.
You can use a simple proto-board to construct this circuit because the components used are simple and only a handful.
In this example, you will notice the circuit board holds some SMD parts. After fixing all the parts, the spirit-level vial can be attached in the optocoupler. If you need it to be immobile, just apply some glue once you have determined the right position and stick it into place.
We recommend constructing this circuit into a small case. This housing will contain the circuit, an on/off switch and a 9-V battery.
The circuit board is attached strategically that it can be moved a little so that the indication can match with an external vial which is attached using adhesives to the outside of the case acting as an extra assistant.
For levelling small objects, you can use this small case. Additionally, you can also fix a spring clamp to a standard spirit level to the case and utilize it as an additional indicator.