Descrete Logic VFD Clock
A new VFD had to be found, thankfully my aunty and an old VHS that was dead that provided the VFD you see to the left. I then worked on finding the pin-out of the VFD using a computer PSU and two AA battery's, I then wrote the notes in my notebook. I also decided to use the only 7 segment driver chips I had thanks to my schooling days.
Welcome to my most complex project to date. The VFD clock was born when I finely found out what the cool display used in VHS'es were. It was called a VFD, I soon learned how to power them. once an interesting component that filled me with wonder the next minute it was going to be involved in one of my two on going ambitious projects. The VFD clock and the portable battery TV.
The first VFD I was going to use was a small one salvaged from an old VHS, but it fell out the cupboard and the nipple broke off thus the vacuum was lost. It eventually found its way onto my car keys until on a dog walk I closed the boot with the hand holding the keys and it went smash on the car. It's now on display in my room. Displayed right.
The basis of the clock would be the HCF4026BE which would be powered by 555 timers. This plan is still the foundation although more then just 555 timers are required, some innovative circuitry. I did want it to be a watch at first as it would be the first VFD watch but microcontrollers would be required for such a circuit. So clock it is!
while initial circuits were set up without any problems other than the ones that come with soldering (solder bridges or mistaken connections) the multiplexer would prove completely different. the first stage or multiplexing is physically dividing the 7 segment lines of each chip (two at the moment) from feeding the VFD at the same time. It found itself dumped my cupboard for until I could find out how to do it. There was a lack of solid core wire but it was not a problem at that time.
Multiplexer V1 came in the form of lots of diodes and resistors from old graphic equaliser boards from 1970's studio equipment. I could not find enough AND gates so I used diodes and resistors to create theses. I built all of them due to lack of breadboard space only to find that it failed horrifically and did not do what I wanted, thus it went in the cupboard agene. Weather AND gate chips will ever have worked I will never know.
About two years in the development having left school and sixth form I fond the first year of collage had gone and I was in the summer holidays, project comes out, I have built a power supply with the help of a very kind course tutor, I try agene and decide to use the prototype the optocouplers. Multiplexer V2 SUCSSES! soldered it onto a circuit board. Had a fight with an optocoupler that died in circuit (caused lots of frustration and anger), some small solder bridges [The arses] and a crappy connector for the VFD I built. In the process of this build I also changed the rats nest wiring to neat plugs and cables from the AMP that I converted into a power supply. This was another first on the list{first multi board circuit, first clock, first use of connectors}. Now the driver for the Multiplexer in in its prototype stage, Its using a 555 for to give a clock signal. An HCF4026BE to drive the negative activated Multiplexer with some 1970s BC212L PNP transistors also off the graphic EQ board to invert the signal to positive to drive the grids the right time. This is the first time I have got transistors to do what I want without help. I've always found chips easy to work with as they do what they say in the datasheet.
The plan is to have the HCF4026BE drive a HCF4053BE multiplexer chip and a second 555 to give me the the 4 output that only activate one at a time. Hopefully this will be done soon and I can sort out the frequency problem I have been having. When the project is finished I will post circuit schematics I created. The HCF4053BE multiplexer failed me as it caused to much ghosting and for some reason cut off one of the segments in the tens digit.
Ok it has been a long time since I have worked on this project, but it is not dead, I am planning to release the schematics on parts which are at there final design to date so if you want to start and develop this device further as well, you can. I'm just finalising the first year of university and then I can get to work on a hole lode of projects I have planed for the summer.
YouTube Channel: http://www.youtube.com/user/TheEPROM9?feature=mhee
This is where the magic has been happening, one never though it would take this long to develop. I have been working on this thing since I was in school at the age of 15 to 16, now I am at university. The set up has improved greatly as I have scavenged lots of new test equipment from university, not all of it out for this project. =-)
The bottom left is my HAMEG HM203-5 20MHz Scope, 20 years old, 1980s. Above that is my home made PSU, has not really been changed much, but had Meany repairs. My PEAK atlas ES60 ESR, LED and battery testers and Solder station sit on that. At the bottom right is my SE SM200 Mk2 Nixie tube Frequency Counter, 40 years, 1972. Above that is my 1975'ish Volt meter. Then my Weir 423D 70s PSU sits on top with one of my multimeters on top.
The rest you can see for your self. =-)
As you can see from the picture we have the new kid on the block, The driver that does the main grunt of swapping between the grills at a high rate, one at a time. Runs at about 1.61KHz to 1.58KHz, this is believed to be caused by the noise on the power supply, the PSU is where I plan to work next. The circuit uses a 555 for the clock, a HCF4017BE to drive the anodes on the VFD. A HCF4011BE is used to invert the grill output to a negative range so it can drive the Opto couperler part of the multiplexer.
I would also like to point out that this project can be considered open source and you can also contribute to the project your self if you want, all I ask is that you credit my design when you use it, with a link, name etc. All notes and documentation can be found on this link, just download the images.
The VFD display multiplexing with my custom bastard of a circuit.
The opto copoler that would isolate the segments driven by the HCF4017BE then inverted by the HCF4011BE to positive so it could drive the grids.
The main multiplexing driver, consits of a 4017 to drive the segment selection & the 4011 inverts the signal for the VFD grad.
Segment switching via opto copolers.
The pinout & revece engineering of the VFD display pulled from an old VCR.
The HCF4026BE driving the VFD directly.