7441 / 74141 nixie driver tester
Schematic - Hand wired proto
Hex File

This tester is essentially a 12 channel A/D with logic setting and power control for the unit under test (UUT).  The Vcc of the UUT is supplied by a pair of GPIOs to provide a 50mA current limit in case the part is dead.  A high voltage bias is switched on during testing to measure both the active low current handling of active outputs as well as the leakage current of inactive outputs.  Data is collected and sent to a PC for processing and Pass/Fail determination which allows the identification patterns as well as device family specific test parameters to be soft coded and stored in a plain text file that can be updated as new devices are encountered.   Test time was about 2 seconds per unit including handling.

Pass  SN74141N (TI)
Pass  7441A (ITT)
Pass  F9513 (FC)
Pass  NS8840 (NS)
Pass  SN7441A (TI)
Fail   7441B (Sig)  Leaky
Fail   7441B (Sig)  Leaky
Fail   7441B (Sig)  Short
Fail   7441B (Sig)  Decode
Fail   7441B (Sig)  Decode
Fail   7441B (Sig)  Decode
Fail   7441B (Sig)  Decode
Fail   7441B (Sig)  Decode

The links to the left are the output screens of the 7441 tester GUI in the Calculators program.  When the button on the box is pressed, both the red and green LEDs are lit and a "Test-me" command is sent to the connected PC.  For each possible input state of 0000 to 1111 the following data are collected:
  • The logic state at the inputs to verify the state set is actually present
  • The voltage at the output of the 72V boost converter (Vbias: For the output pin voltages, the leakage current is approximately 16uA per volt of drop below Vbias)
  • The UUT VCC
  • The voltage present at every output pin

After all 150 pin combinations are measured, the logic high (1) or low (0) for each state is determined from the selected parameter set.  Any pin that is in between a valid logic high or logic low is grayed out and given an "X" in the pattern window.  The resulting pattern of 1's and 0's (Any "X" is an automatic "Fail") is then compared against known device patterns and if a match is found then the red LED is turned off indicating a "Pass" or else the green LED is turned off indicating a "Fail".

  Any questions or comments?
This page last updated on June 08, 2009