Re: Fast (simple) beam break detector

On a sunny day (Thu, 02 Oct 2008 21:45:14 GMT) it happened Rich Grise
<rich@xxxxxxxxxxx> wrote in <pan.2008.10.02.22.45.12.542478@xxxxxxxxxxx>:

Or, you could draw a backwards scale on the meter, for speed; meter 0
would correspond to infinite speed, of course. ;-)

Oh, yes, I forgot that late last night, we will use a second 4016 switch
(it has 4 after all) to disconnect the meter when no shot is detected.
And an other one to disable the current source if no shot detected to save power :-)
So, now 1 74HC4016 switch left, do not want to use it for Q1, as Ron can be
as high as 150 Ohms...
OK, save more power: Switch of P3 :-)


Corrected version:

+ +
| |
e PNP e PNP
b--- b- Q3
c | c |
| Q2 | |----
-------| ---|
!trigger 1 ------------- set | |-- |
74HC74 c | | |
!trigger 2--R7 -------- reset !Q --- R1------b NPN === | R2
| e Q1 | | | charge
a FF1 | | | [ ]<--- current
diode pulse former /// /// | | P1 |
k D1 | 0 / 4016
| C1 | /------------------------
from reset other FF | 0 |
---------------------------------------------------------- | |
| charge switch current mirror /// |
| |
| peak detection and hold |
----- + + |
opamp1 out--- | 4016 |
----- - | 0 / |
| D2 | 4016 / --------------|
|--------k diode a --- meter \ 0 |
|---------------------------------------- + / \ | |
=== | opamp2 out ------R4 --- O ---0 0-->[ ] meter bias |
| C2 0 / -- - | | | P3 |
/// / ---------------- | R3 | /// |
0 | | | | |
| | -----------------| | |
/// | | | | |
4016 | gain --->[ ] P2 | |
discharge switch | | gain | |
| /// | |
| | |
| | |
!trigger 1 ----------- set Q--^-----------------------------------------------------------------
74HC74 | L1
+ -- R5------ reset !Q --- R6-------- k LED a ---- +
| FF2 shot detected light
/ reset button
| S1
/// shot detector

R1 4k7
R2 1k
R3 10k
R4 depends on meter sensitivity, 5 V for full scale... if 100 uA then 50k
R5 10k
R6 4k7
R7 4k4

P1 10k
P2 10k ?
P3 2k2

C1 depends on distance (pulse-length and current)
C2 1nF poly

D1,2 1N4148

Supply +5V (use CMOS opamps).


Something like this (photo detectors not drawn).

Drawing errors?

trigger1 low will set both FF.
Pushing S1 the reset button will reset both FF.
When FF1 is set, Q1 stops conducting, and C1 is charged by Q2 with a constant current.
Opamp1 charges C2 to the peak voltage, and holds, opamp2 buffers and has some gain if needed.
The 4016 switch discharges C2 upon pressing reset.
LED L1 indicates a shot was detected.

All values are 'guess values'.


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