Automatic Hallway Light [Suggestions/Advice]

Thread Starter

Arausio

Joined Jun 18, 2015
41
Hi Eric,

Here are my results:

1. Disconnect R19 from the IC4A pin#7.
Connect the free end of R19 to +5V, the relay should operate.
If it operates OK, then reconnect R19 to pin#7 of the IC4A.


The relay toggled and white LED illuminated.


2. Check that IC4A have +5v on pins 5,2,1 & pin#3 is 0V
Disconnect the link from pin#3 of the 555, that connects to IC4A pin #4

Touching the free end of the link to +5V should switch the output pin#7 of the IC4A and operate the relay.
If it operates OK [ it may 'chatter' because of the crude way of touching the +5V with the link]


Pins 5, 2, 1 do have +5V and pin 3 has 0V. I disconnected the link from pin#3 of IC2, with the opposite end still connected to IC4A pin #4, and touched the free end of that link to +5V. Relay did not toggle.


3. Check that IC2 the 555 has +5V on pins 4,2,8 and that R16 & C5 are correct.
Touching pin#2 of the 555 to 0V should trigger the 555 and operate the relay.


Pins 4, 2, 8 do have +5V and R16 and C5 are correct. When I touched pin#2 of IC2 to 0V, LED2 (GREEN) illuminated but the relay did not toggle.

It looks to me like the problem is with IC4A. I have attached an image of my IC4A connections and a data sheet for it. Is there additional set-up that needs to be performed with IC4A?
 

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ericgibbs

Joined Jan 29, 2010
18,766
hi A,
I can see why the LS109A is not switching, the power pins Vss pin#16 [+5V] and Gnd/0v pin #8 are not connected.
There are missing from the Original circuit diagram.!!

E

EDIT:
Added marked up diagram,
Shows the LS109A power pins.
add the decoupling on the +5V rail.
 

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Last edited:

Thread Starter

Arausio

Joined Jun 18, 2015
41
Eric,


It worked! Thanks a lot for your help.

The entire circuit works as expected now, although the white LED illuminates as soon as I turn on 5V supply. Maybe there is a way to reset the IC4A to a known state as mentioned by AnalogKid? The demonstration video is below. Now, I have additional questions:

1. IC1 is configured in astable operation and IC2 is configured in monostable. Could both IC1 and IC2 be configured in monostable or astable?

2. What is the importance of decoupling? What function does it provide?

Functional Demonstration:
 

ericgibbs

Joined Jan 29, 2010
18,766
1. IC1 is configured in astable operation and IC2 is configured in monostable. Could both IC1 and IC2 be configured in monostable or astable?
2. What is the importance of decoupling? What function does it provide?
hi A,
The link posted by 'dj' covers the decoupling requirement.

IC1 as an Astable generates the pulse drive for the IR Emitters.
IC2, when triggered by a beam break generates a ~1Sec long clock pulse for the LS109A Bistable.
I do not follow why you ask Could both IC1 and IC2 be configured in monostable or astable?

I agree with 'ak' a power On reset for the LS109A should be added.
At the moment the only way to Clear a On state at power On is to pass your hand thru the IR beam and interrupt it.

E
 

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Thread Starter

Arausio

Joined Jun 18, 2015
41
Hi Eric,
I received the 22nF capacitor from digikey and together with 4.7k resistor tried assembling the 'power-on reset' for the LS109A. The circuit, however, still functions as before. The white LED illuminated any time I turned on my 5Vdc power supply. Why did you choose those particular values of capacitance and resistance? How would I correct this circuit to have the 'power-on reset' function?
 

ericgibbs

Joined Jan 29, 2010
18,766
How would I correct this circuit to have the 'power-on reset' function?
hi A,
You could add a manual Reset push button across the 22nF capacitor.
Also try increasing the 22nF value to say 1uF, the fail to to power on reset, maybe due to a long settling time of the circuit.
E
 
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