IV-12 VFD Socket Solution. (Because 10 Doesn’t Fit 9, and They’re All 9.)

After recieving the miniature tube sockets, it was shocking to realize a 10 pin tube doesn’t fit into a 9 pin socket. So, next time count better and don’t assume all little tubes are the same. After checking around, it seems 10 pin preamp size tube sockets dont exist much, if at all.

Digi-Key was also little help. Acceptable pin sockets were $20-40 in cost for 60, for solder tails and proper size compatibility. Socket footprints also complicated things, as spacing between the pins is minimal. The cheap solution: pull the pin sockets out of the unusable 9pin tube sockets. 100 pin, for about $14.

The tube sockets from Parts Express are described as porcelain style. They’re white plastic.

Posted by rmrubin Posted in: Electronics Comments Off October 2007

VFD Clock PSU Schematics. Darlingtons and Transistors, and Stuff.

Finalized VFD Radio Clock power supply schematics. Shopping is 90% complete. The discrete linear regulators cost about $0.80 in parts, not including voltage transient supression devices.

The first schematic includes the fused IEC power entry module and the DPST power switch. The switch selected is a green illuminated rocker by Cherry Switch Company. The second schematic is the unregulated section of the power supply. The third is the linear regulator section.

Transient voltage suppressor (TVS) varistors are used in parallel with the transformer primary coils, after the rectifier bridges, and on the outputs of the regulated supplies. Schottkys are used on the unregulated and regulated supply outputs to suppress reverse polarity voltage transients. All regulated outputs are fused.

Caps were selected to keep ripple voltage well above the dropout voltages of the linear series pass regulators. R3 is a high watt resistor used to decrease loading of the linear output transistor, and provides some current limiting in the event of an output short. All caps less than 1uF are for EMI supplession. MMBT4403 (PNP BJTs) Q1 and Q2 form a current source for the MMBT4401 (NPN BJT) Q3 Vbe multiplier, which is the voltage reference for the TIP122 (NPN Darlington) Q4 pass transistor.

The current source is to increase PSRR, allowing a stable Q3 Ice, and thus a stable Q3 Vbe. Darlington transistors are used for the low Ibe current, further stabilizing Q3 Ice, Vbe and Q4 Vbb with fluctuations in Q4 Ice. The majority of Vout error is likely to be caused by variations in Q4 Vbe created by fluctuations in Q4 Ice. Temperature changes of Vbe in Q4 and Q3 will also contribute to Vout error. Although Vbe changes due to temperature in both devices might be similar, the multiplication of Q3 Vbe as Q4 base reference makes it unpredictable as temperature compensation.

The negative supply is like the positive, but flipped, using a TIP127 (PNP Darlington), and without the high watt resistor. Vcc is much closer to Vee, so less power is dissipated. However, it makes the negative unregulated supply decoupling caps much more important, as these are not LDO type regulators and have an expected dropout of 2V-2.5V.

The -25V supply is for the VFD anodes and grids via the VFD driver IC.

The 5V will power the AVR controller, the VFD/IO chip logic section, and the WWVB reciever IC. WWVB receiver and AVR AVcc power will come thru a 1000uH coil.

The 1.5V supply is for the cathode filaments of the VFD tubes.

Posted by rmrubin Posted in: Electronics Comments Off October 2007

VFD Controller IC Plus Cake, Serial Interface

Found by kevtris on the Digi-Key: STM86312 (497-4363-ND), a multiplexed VFD tube driver, with switch input, keyboard matrix input, LED output, and a 4 pin serial interface. Basically, everything for the VFD radio clock besides wwvb decoding and the uC to figure it all out.

STM86312 VFD Driver w/ LED and Switch IO Datasheet

Posted by rmrubin Posted in: Electronics Comments Off October 2007

In Soviet Russia, 7 Segment VFD “Nixie” Tubes Ship You

The 7 segment VFD tubes won on ebay have arrived, from Moscow, Russia, Canada. Apperently their business office is in Canada, but the warehouse is in Russia. On first glance, they look okay. No obvious cracks or frosted getters. Very sexy lookin, looking forward to testing them after sockets have been purchased.

Posted by rmrubin Posted in: Electronics Comments Off October 2007