Thank you for purchasing the Bolt Industries VFD clock soldering kit! Here you will find detailed assembly instructions, schematics and pictures for each layer as well as a troubleshooting guide. The clock does not need to be assembled in a particular order, however it is recommended to go from the bottom up. If you’re looking for the open source design, it is on our open source projects page.
If you need help troubleshooting or have questions, please send an email to ian@boltind.com
The Most Important step
The blue potentiometer on the left side of the VFD layer controls the voltage to the VFD tube grid. The range is about 0-45 VDC. Turn the potentiometer all the way counterclockwise prior to powering on the clock. Starting with a higher voltage will shorten the life of the tubes dramatically.
Also, it’s important to note that some of the pin headers face up and some face down. Soldering a header on the wrong side of the board will ruin your whole day, so make sure to get them on the right side.
About the VFD layer resistors
If you choose to skip the instructions and go straight for assembly, that will work just fine however you’ll probably be confused about the resistors on the top layer. Your VFD tubes should come packed with the correct resistors that are sized to match your VFD tubes. For IV-6 tubes, R1-8 are all 47Ω. For IV-3A tubes, you should have four 91Ω resistors, and four 62Ω resistors. One value goes in the row behind the tubes, the other value is for the block of 4 resistors in the front. So R1-R4 are 91Ω and R5-R8 are 62Ω. The other way around is fine too. It does not matter where each value goes, as long as they are all the same on each side. The end result is that there’s one of each resistor value in series with each VFD heater filament.
You’ll need a power supply
The clock requires a 5 volt micro USB power supply rated for at least 1.5A. The clock draws .5A continuously. A smaller cheaper power supply will work but it will run hot and the tubes will be dim. A bigger USB power supply like the ones that commonly come with phones and tablets works best.
Layer 0: The bottom cover.
There’s no soldering to do on this layer. Just install the hardware.
Layer 1: The main Binary Coded Decimal clock
All components and headers on this layer must face up. Solder all components in their place. The 32.768Khz crystal needs to be soldered, and it’s case must be glued to the PCB. If it’s case is left free floating it will not keep time accurately.
Layer 1, option A. TTL Logic clock.
Assembly is straightforward. Place all IC’s in their proper place and solder them in. All headers face up. The 32.768Khz crystal oscillator’s case must be glued firmly to the PCB for accurate timekeeping. If your ones digits get stuck at zero this is caused by a hardware bug. Send us an email and we’ll mail you these capacitors free of charge. The image below shows where to put them.
Layer 1 option B: Raspberry Pi Pico software driven clock.
Firmware for Raspberry Pi Pico driven clock:
Layer 2: Binary Coded Decimal to 7 segment decoder or 4 bit BCD display
Some of the headers face up and some face down on this layer. See the example below. The same is true of the LED’s. Other BCD displays are at the bottom of the page.
Layer 3: 7 Segment VFD Display
For this layer, there are several surface mounted components. It is advisable to solder these first. When soldering the VFD tubes, it is somewhat difficult to get them all straight. There are two 3d printable jigs that can be downloaded below to assist with this.
VFD tubes, just like any other vacuum tube have a heater filament. A VFD tube’s heater filament needs a minimal amount of current flow. Each manufacturer’s heater filaments have a slightly different impedance. Your resistors should be packed in the same bag as your VFD tubes. If you purchased multiple kits, be sure not to mix these resistors. You will find two resistor values packed with your VFD tubes. The four resistors toward the front must all be one of these values, and the other four resistors go behind the VFD tubes. If you look at the schematic below, you’ll see that there’s two resistors in series with each heater filament. A single 100Ω resistor in series with the heater filament would work just fine, but this dissipates too much heat in one place and it gets really HOT. Two resistors spread out tends to run cooler and allows for a much more precise control of the heater current.
Tip: Trim the leads of each VFD tube each at varying lengths. This makes them a lot easier to slide into the PCB.
Download a 3D printable jig to hold your VFD tubes straight while soldering here:
Optional Layers
5mm Binary Coded Decimal LED display
Assembly of this layer is straightforward, but reading the time is not. To read the time, the value of the digits that are lit in each column must be added together. In the example below, the time is 12:57:32.
HDSP display layer
HDSP displays are rated for 5 volts but they tend to run really HOT at 5 volts. To extend their lifespan, a small resistor can be placed in series with the VCC pin. The ideal value will vary. I’ve found the best value is about 20-100Ω. If you’re using authentic HP HDSP displays, then odds are that they will have beautifully gold plated pins. Try to use only a minimum amount of solder to avoid covering up the beautiful gold finish of the PCB and the HDSP pins. The two blue capacitors are purely decorative. The cool looking surface mount switches look really cool, but they tend to be a little bit more bouncy than a regular through hole tactile switch. it may take a few tries to get the correct time.
7 segment LED display
Assembly of this layer is straightforward. Just solder the components and turn it on.
Troubleshooting Guide
The following are some common issues you may encounter and how to correct them. If you need assistance, please create a post in the Bolt Industries community forum HERE.
| Problem | Solution |
| The clock doesn’t keep time accurately. | The 32.768Khz crystal must have it’s case glued to the PCB. |
| The clock counts about twice as fast as it should. | The CD4060 14 stage ripple counter probably got a zap of static electricity. Contact us for a replacement. |
| None of the VFD tubes light up. | Check the step up converter’s voltage output. Increase the potentiometer set point by turning it clockwise. Check that there’s both 5VDC and Gnd present on the third layer. Also check for 5 volts on the first layer with a multi meter, or by connecting a 5mm BCD LED display layer. A bad solder joint on the micro USB connector is a likely possibility. See the schematic for where to connect multi meter probes. Does the LED under glow on layer 2 turn on? If so, does it get dimmer when you turn on the toggle switch on layer 3? This can only be a solder bridge on the VFD layer. |
| One or more VFD tube is not lit. | Check for a cold connection on the tube’s leads and the filament resistors by the tubes. |
| A tube displays a garbage digit. | One of the 74LS48 BCD to seven segment decoders has suffered electrostatic damage. Contact us for a replacement. |
| The hours are higher than 12 or 24 | The 12/24 switch was probably toggled from 24 to 12 while the hours were higher than 12. The count will not reset to 1 until it reaches 99. Power the clock off and turn it on again. |
| My clock runs hot | This is normal. The IV-6 version runs even hotter than the IV-3A version. |
| I cracked one of my VFD tubes | Contact us for a new tube. The best way to de solder a VFD tube is with a hot air reflow station. You can also cut each pin with a pair of cutters, then suck the remaining pin and solder out with a solder sucker. You can also send your clock back to us and we’ll replace the tube for you. |
| My one’s digits get stuck at zero | This is a hardware bug that affects the TTL clock. Unfortunately there is something different about the quad 2 input AND gates that were used during the prototype phase and the AND gates that were sent out with the clock kits. The solution is to add a .01μF capacitor to the inputs of the AND gate that advances the one’s digits. Send us an email, and we’ll send you the capacitors free of charge. |
