Please Be Discrete

January 20, 2011 by

The 555contest has triggered (pun!)  a desire to be discrete. No, im not talking about conservative speech or keeping secrets, im talking individual componants!

It looks like im not alone! Someone has already been looking into this on Dave Jones’s eevblog

The forum user has linked to a schematic which may have been used to digitaly simulate the inner workings of the 555 timer.

I recall using a tool called (Circuit builder?) in high school to design basic digital/analog circuits. I wonder if i still have it installed on an old laptop somewhere…

My goals:
Reverse engineer the inner workings of a 555 timer chip.
Build a functioning 555 timer chip with “socket” extension that can be plugged into various “test boards”.
Make 2-3 test boards (blinky lights, pwm controller, one shot/debounce)
Design and etch clean looking boards for the 555 and test boards

Simulation software (circuit builder, pspice or lt spice)
Circuit board design software (eagle)

Linear Technology LTspice IV …examples\Educational\NE555.asc

Parts list (potential):
Transistors: BC847B (NPN ones) and BC857B (PNP ones)
Q1 N5 5 N7 1 NP
Q2 N1 6 N6 1 NP
Q3 N1 N6 N8 1 NP
Q4 N5 N7 N8 1 NP
Q5 7 N16 1 1 NP
Q6 N17 N14 1 1 NP
Q7 N1 N1 N3 1 PN
Q8 N17 N1 N2 1 PN
Q9 1 N5 N2 1 PN
Q10 N5 N5 N4 1 PN
Q11 N11 N20 N9 1 PN
R1 8 N3 4.7K
R2 8 N2 830
R3 8 N4 4.7K
R4 8 N9 1K
R5 8 5 5K
R6 8 N22 6.8K
Q13 1 2 N10 1 PN
Q14 N14 N10 N11 1 PN
Q15 N13 N12 N11 1 PN
Q16 N13 N15 N12 1 PN
R7 N14 1 100K
R8 N13 1 100K
R9 N15 5 5K
R10 N15 1 5K
R11 N8 1 10K
Q17 N16 4 N18 1 PN
Q18 N19 N17 1 1 NP
R12 N18 N20 5K
Q19 N20 N20 8 1 PN
Q20 N21 N20 8 1 PN
Q21 N21 N19 1 1 NP
R13 N17 N21 4.7K
Q22 8 N22 N23 1 NP
Q23 N22 N21 N24 1 NP
Q24 8 N23 3 1 NP
R14 3 N23 3.9K
Q25 3 N25 1 1 NP
R15 N25 N24 220
R16 1 N24 4.7K
R17 N24 N16 10K
D2 3 N22 D
D1 N18 N19 D
.MODEL NP NPN(BF=125 Cje=.5p Cjc=.5p Rb=500)
.MODEL PN LPNP(BF=25 Cje=.3p Cjc=1.5p Rb=250)
.MODEL D D(Is=1e-12 Cjo=1p Rs=5

to be updated as the project procedes!


One Comment on Please Be Discrete

  1. admin on Mon, 26th Sep 2011 9:15 am
  2. FAIL. never did it.