Tag: PCB
The slow ticking clock.
by Jae686 on Jan.18, 2012, under Electronics, Nixie Clock
And all was good. The latest version of the nixie clock survived it’s smoke test, and, as usual, I’ve let it powered for a while and then something quite awkward started to happen : The clock always got consistently late. Its was quite odd, since most of the PCB remained the same, except for the inclusion of the Nixie Power Supply and the re-positioning of several traces and components.
The fact that the failure is consistent leads me to believe that it should not be related to the Nixie’s HV PSU presence on the same PCB as the RTC. And the fact that the seconds are twice as slow (a consistent behavior) is clearly measurable.
After some digging, I’m inclined to believe that the root cause for the clock not behaving as expected was due to the pcb track re-routing. When re-routing the PCB traces, some traces passed very close the the RTC’s crystal pins. And yes, this is noted on Maxim’s RTC’s aplication notes.
Well, back to PCB etching!
Fixed design : GND guard ring around the RTC, and the traces were re-routed to avoid being close to the cristal.
Versions and a Last Revision
by Jae686 on Jan.06, 2012, under Electronics, Nixie Clock
The 2nd version of the nixie clock was done. The PCB’s were good, the EMI issue traced and fixed, therefore the clock met all specifications I’ve set for it.
Nixie Clock Version 2
Or not quite.
At First the ideia of having 3 diferent PCB’s made sense, since each board had a specific function (Nixie and Driver PCB, µC Pcb, User IO PCB), but this aproach led to a awkward configuration to make or find a proper housing for. And there is still the issue of the PSU shielding, should the enclosure not allow for a bigger space between the PSU and the µC Pcb.
Not to mention the fact that I don’t have proper tools to cut the PCB’s, leading to some work to cut the PCB in 3 pieces for the Driver, µC and user IO PCB’s.
Therefore I’ve decided to make a incremental change to the Schematic and PCB design of the 2nd version of the clock.
HV Nixie PSU Breadboard Prototype
The goals I had in mind for the last revision of the clock were to :
- Have the Nixie PSU on the µC PCB, instead of a separate, pre-build PSU.
- Have the clock built in such way that it would be pleasing to look at, even when using a transparent enclosure.
On the PSU side, instead of designing one from scratch (and I seriously doubt that it would be trivial….) I’ve decided to use this schematic instead. The main reason was the lack of exotic components
I was not able to use the exact value for the inductor, but once the prototype worked, the PCB design was changed to accommodate the power supply . Previous testing with the power supply suggested that, as long as the PSU is far enough from the RTC and the I2C bus, I would have no EMI problems (before the testing I was considering using metal shielding on the PSU to avoid EMI issues).
Nixie Clock Version 2 PCB alignment check
On the “Pleasing to look” at side, since the PSU and the µC are on the same PCB, the user IO board, with a PCF8574 IO expander and some pull up resistors, was also put onto the same PCB. Therefore, the clock was condensed to only 2 PCB’s.
The connector between the Nixie board and the µC board was , along with the screw holes, aligned in order to be possible to assemble them as shown on the left photograph.
Nixie Clock Version 2 PCB (µC, PSU and User IO)
When the PSU and User IO boards were combined, I was able to better use the PCB’s surface area, since I could put the components as close as I could , regardless of their function.
Any new Hardware features may still be added without modifying the PCB layout, since the I2C bus is exposed by a 5 Pin Header.
Detail of Nixie Clock during assembly
Smoke Test of the PCB. The Nixie Diver board is the same from version 2 (they are compatible).
