Small Brains Engineering`s Numitron Clock Users Manual
Contents
1. 20 MHz in 28 pin DIP socket RTC Dallas DS1307 I C RTC with CR 2032 cell Time base 32 768 KHz crystal Epson C 2 Type 20 PPM Power consumption Approx 0 180 to 0 220 A 12 VDC input Power connection 2 1mm 12 VDC center positive reverse protected Technical Information This section is for people who wish to customize their clocks by replacing the stock microprocessor with one containing their own firmware The stock microprocessor is a PIC16F876A I SP using a 20 MHz ceramic resonator Pin 2 is used as an analog input for the light level sensor all other pins are configured for digital I O Any pin compatible PIC may be used I O Assignments PORTA analog and digital inputs A 0 Light level sensor ADC input Lower darker higher brighter A 1 H SET button 0 pressed 1 not pressed A 2 M SET button 0 pressed 1 not pressed A 3 12 24 button 0 pressed 1 not pressed A 4 SWQ signal input from DS1307 10 K ohm pull up to 5V PORTB segment driver outputs B 0 DP Segment 0 dark 1 lit B 1 Segment A 0 dark 1 lit B 2 Segment B 0 dark 1 lit B 3 Segment C 0 dark 1 lit B 4 Segment D 0 dark 1 lit B 5 Segment E 0 dark 1 lit B 6 Segment F 0 dark 1 lit B 7 Segment G 0 dark 1 lit PORTC digit driver outputs and lC bus C 0 ones of seconds drive 0 dark 1 lit C 1 tens of seconds drive 0 d2. as a PM indicator when the clock is set for 12 hour mode Your clock will automatically dim and brighten the display tubes to match the ambient light level For best appearance and tube life you should avoid direct sunlight 12 Hour and 24 Hour modes The clock can be set to display the time in either 12 Hour or 24 Hour format by pressing the 12 24 button Tube Saver Mode You can put the clock into or out of a tube saver mode to conserve power and extend the lifetime of the Numitron tubes by pressing the TUBE SAV button The digit separator marks will flash in sequence like the swinging pendulum of a mechanical clock to show the clock is powered up and running Tube Saver mode is ideal if you re away for the weekend or on a short vacation If your clock is not going to be used for an extended time it should be unplugged Setting the Clock When the H SET button is pressed the hours value will increase The value will increase slowly at first and then speed up if the button is held down When the M SET button is pressed the minutes value will increase and the seconds value will be set to zero The value will increase slowly at first then speed up if the button is held down If the minutes value wraps around from 59 to 00 the hours value will not be incremented To set the clock accurately set the minutes value to the current minute As your reference clock wraps around from 59 to 00 seconds click the M SET button to increment the
3. Small Brains Engineering s Numitron Clock User s Manual This handmade digital desk clock uses six NOS new old stock Russian surplus IV 9 Numitron display tubes to display the time with glowing metal filaments suspended in glass vacuum tubes What is a Numitron Numitrons are an obsolete digital display technology introduced in the early 1970 s Essentially a specialized version of Edison s original electric light Numitrons glow with a warmth unlike any modern display Built like vacuum tubes yet driven directly by low voltage logic Numitrons were a transitional technology bridging the eras of radio tubes and digital logic Numitrons competed with the older and more common Nixie tubes but were quickly made obsolete by the introduction of the modern LED display As a result Numitron displays are quite rare today Operation j f F e j 4 E 4 mey kemp S 7 s fa _f 42 s t4 ou Gage SER LEDU toa gt t 543 FEFTTTFTTFEEFEFENTETEFEEE EN oe Ae T D 12 24 tuse sew Co yer te a e E EEE CEA 12 24 Hrs Mode The Display Your Numitron Clock displays the time using six IV 9 Numitron display tubes Each tube can display a single digit and a digit separator mark The digit separators in the ones of hours and ones of minutes tubes flash once per second The separator marks are lit during the second half of each second The digit separator mark in the ones of seconds tube is used
4. ark 1 lit C 2 ones of minutes drive 0 dark 1 lit C 3 I2C bus SCL 4 7 K Ohm pull up to 5V C 4 I2C bus SDA 4 7 K Ohm pull up to 5V C 5 tens of minutes drive 0 dark 1 lit C 6 ones of hours drive 0 dark 1 lit C 7 tens of hours drive O dark 1 lit Recommended Multiplexing Timing The display tubes are multiplexed so that only a single tube has its drive signal PORTC on for a 4 millisecond window out of every 24 milliseconds This yields a refresh rate of about 41 6 Hz Each tube has a maximum duty cycle of 16 6 for full brightness and a 8 3 duty cycle at full dimming To give a reasonable brightness at this duty cycle the Numitron drive voltage is regulated to about 8 5 volts Any custom firmware must ensure that the tubes are not over driven duty cycle too high to prevent premature tube failure Also the power supply is designed to drive a single tube at a time Enabling more than one digit drive signal at a time may cause excessive current demand and heat To drive the display the microprocessor must set PORTB to select the desired pattern of segments and then pulse the desired digit drive output high Current will now flow through the Numitron tube and the filaments will glow The longer the digit drive signal remains high the brighter the filaments will glow Turn off the digit drive signal and begin the process on the next tube to be driven For best tube life each tube shou
5. ck uses a CR 2032 coin cell battery to maintain timekeeping without external power This battery will drive the DS1307 time keeping chip for over 10 years without external power The backup battery may be replaced by a competent electronic technician by following this procedure 1 Disconnect external power and carefully remove and store the acrylic cover 2 Carefully lift the base of the clock and remove the four screws and washers mounting the electronics to the base The Numitron tubes must be protected from any shock or impact 3 Lift the electronics from the base a few inches by letting the power cable slide through the hole in the base You can now see the CR 2032 coin cell in its battery holder on the bottom of the electronics module 4 Remove the old battery and inspect the contacts for any leakage If your battery has leaked please contact us for service 5 Install a fresh battery into the holder plus side facing away from the socket and place the electronics module back onto the base and replace the mounting screws and washers 6 Reconnect the external power and reset the clock Verify that the clock will continue to keep time while the external power is disconnected If all is well replace the acrylic cover Specifications Size 5 wide 4 tall 3 4 deep inches Numitron type Russian type UB 9 IV 9 multiplex drive 8 5V Digit Size Approx 0 45 tall 0 26 wide Microprocessor Microchip PIC
6. ld be driven with the duty cycle between 8 3 and 16 6 IV 9 and other Numitrons may be subject to mechanical resonances in the filaments that can drastically shorten the tubes life We recommend using the 8 3 to 16 6 duty cycles with the stock refresh rate of 41 6 Hz
7. may effect the accuracy of your clock If the base and electronics become contaminated we recommend you contact us for service Customizing your clock There are several ways you might like to customize your clock Photographs or colored backgrounds may be placed on the inside of the acrylic case behind the tubes Window tinting films or colored filters could be used to enhance contrast and give your clock an even more unique appearance For the hard core techie the Technical Information and Specifications sections provide information on how to drive the Numitrons with custom microprocessor firmware Custom firmware could be used to display the date stored in the RTC chip or other information Service Each Small Brains Engineering Numitron Clock is a hand made individually serialized piece of electronic art and we will service these clocks as long as we are physically able to do so For service information please email SmallBrainsLabS comcast net Numitron Replacement Numitrons may last over 100 000 hours of operation over 11 years This clock drives the tubes conservatively especially in lower lighting levels for an even longer life Eventually a segment will fail but this is not a major problem Small Brains Engineering stocks a large number of spare Numitron tubes We can replace failed tubes or provide replacement tubes to competent electronics technicians to service our clocks Backup Battery Replacement This clo
8. minutes value to the current time and reset the seconds value to 00 The hours value may be set before or after setting the minutes value The digit separator in the one of seconds tube will be lit wnen the clock is set for 12 hour mode and the time is past mid day The clock may be set in either 12 hour or 24 hour modes Care and Cleaning The Numitron clock is designed for indoor use away from direct sunlight It should not be subjected to weather or high levels of shock or vibration Acrylic cover Acrylic should never be cleaned with any cleaner containing ammonia such as common cleaners like Windex or Formula 409 Also never clean the acrylic cover with a dry cloth or with your hand as this simply rubs dust and dirt into the plastic First blow off any dust then use a soft cloth with a diluted solution of mild dish detergent and warm water It is even better to use a cleaner specifically recommended for acrylic such as Novus 1 or Brillianize plastic cleaners Base and Electronics The acrylic cover should be used to keep dust out of the base and electronics section as well as to protect the Numitron tubes from damage Should the electronics section need cleaning great care must be used to prevent damage to the Numitron tubes and the clock s time base crystal which is located just to the right of and behind the 12 24 button It is the slender vertical silver tube and it is quite sensitive Any shock or damage
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