Did some "reverse engineering" on the driver part of the device introduced in a recent post and "designed" (ahem…) a new driver circuit based on my findings. See some amazingly craptastic ASCII art below.
Q1..Q7 BC327
Q8..Q14 TIP32C
IC1 74LS138
R1..R7 220 OHMS
IC1
·-------· ·---------·
! ! ! !
! Q8 ! Q1 ! !
b e ! !
ARRAY 0 --c e-· b-----|R1|------ O0 Vcc ----- +5V
! c !(15) (16)!
! ! ! !
+5V GND ! !
! !
·-------· ! !
! ! ! !
! Q9 ! Q2 ! !
b e ! !
ARRAY 1 --c e-· b-----|R2|------ O1 GND ----- GND
! c !(14) (8) !
! ! ! !
+5V GND ! !
! !
·-------· ! !
! ! ! !
! Q10 ! Q3 ! !
b e ! !
ARRAY 2 --c e-· b-----|R3|------ O2 E1 ----- GND
! c !(13) (4) !
! ! ! !
+5V GND ! !
! !
·-------· ! !
! ! ! !
! Q11 ! Q4 ! !
b e ! !
ARRAY 3 --c e-· b-----|R4|------ O3 E2 ----- GND
! c !(12) (5) !
! ! ! !
+5V GND ! !
! !
·-------· ! !
! ! ! !
! Q12 ! Q5 ! !
b e ! !
ARRAY 4 --c e-· b-----|R5|------ O4 E3 ----- ARDUINO PIN 2
! c !(11) (6) !
! ! ! !
+5V GND ! !
! !
·-------· ! !
! ! ! !
! Q13 ! Q6 ! !
b e ! !
ARRAY 5 --c e-· b-----|R6|------ O5 A0 ----- ARDUINO PIN 5
! c !(10) (1) !
! ! ! !
+5V GND ! !
! !
·-------· ! !
! ! ! !
! Q14 ! Q7 ! !
b e ! !
ARRAY 6 --c e-· b-----|R7|------ O6 A1 ----- ARDUINO PIN 6
! c !(9) (2) !
! ! ! !
+5V GND ! !
! !
! !
! !
! !
! A2 ----- ARDUINO PIN 7
! (3) !
! !
! !
! !
··--------·
DATA ------------------------------------------ ARDUINO PIN 4
CLOCK ------------------------------------------ ARDUINO PIN 3
On the right side is the part that connects to Arduino: pins 5…7 select which one of the LED arrays will be lit and pin 2 enables the 74138 output. Arduino pin 4 feeds data to shift registers in the display part; pin 3 clocks them. (Note to self: check that clock part; how much current will 74164's draw?)
Note to self: add resistors between BC327 emitter and TIP32C base.
74138 truth table is as follows:
I N P U T S O U T P U T S ------+-------+---------------- E E E ! A A A ! O O O O O O O O 1 2 3 ! 0 1 2 ! 0 1 2 3 4 5 6 7 - - - + - - - + - - - - - - - - H X X ! X X X ! H H H H H H H H X H X ! X X X ! H H H H H H H H X X L ! X X X ! H H H H H H H H L L H ! L L L ! L H H H H H H H L L H ! H L L ! H L H H H H H H L L H ! L H L ! H H L H H H H H L L H ! H H L ! H H H L H H H H L L H ! L L H ! H H H H L H H H L L H ! H L H ! H H H H H L H H L L H ! L H H ! H H H H H H L H L L H ! H H H ! H H H H H H H L
As can be seen the 74138 outputs (pins 9…15) are active-low. The outputs drive BC327 (PNP) transistors, which then drive TIP32C (PNP) transistors. TIP32C's drive the display modules.
