Author Andrei
31/05/2019
We have another amazin watch project this week. Pakue user psoted on instructables his work. He says that the whole project started a while back with an hackaday article from 2014 in which [Johngineer] build the 'ChronodeVFD', a wristwatch made from an old soviet vacuum fluorescent display. It kind of triggered the 'shut up and take my money' reflex in him, but as it wasn't for sale and he didn't had any design details available, he quickly had to scrap that.

So he explains what is an VFD and How Does It Work, the tests he made in order to make this project, he shows us the Circuit Design and PCB Layout and final assembly and some Troubleshooting.

Vacuum fluorescent displays work kind of like a CRTs where accelerated electrons are bombarded on a layer of phosphor which then emits this typical blue-greenish light. VFDs are driven with much lower voltages compared to CRTs which is why they are often found in small consumer equipment predating the LCD-era. In order to create free electrons a filament is heated within the VFD, the cathode (at negative, or in our case ground potential). This creates an electron cloud around the filament, which will be accelerated towards any positively charged surface, here the plates of the anode. This on its own works already, but would require a separate pin for each segment on the display to drive it. To reduce the number of inputs, most VFDs are multiplexed with a matrix above each substructure like a 7-segment. Only when the plate and its matrix are at a positive voltage electrons will hit the phosphor surface.

The watch was designed with the following specifications in mind:

● Run (briefly) from a AA alkaline battery
● Compact size
● Wifi and Bluetooth
● Easily programmable

Apart this post, if you have your own project and you need good quality PCBs, consider using the services of PCBGOGO.com which will offer you quite good services, I use their services a lot of my PCBs.

Consider supporting ELECTRONOOBS on PATREEON.