• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Please explain capacitor action in this circuit

Status
Not open for further replies.

haxxx

New Member
I found this circuit which detects guest arrival.
Could anyone please explain the action of the capacitors, in the circuit on the right, when the path between the led and the tsop1736 is broken.
Also the datasheet for the tsop suggests using a rc network across pin 1
and 2 of the tsop to suppress power supply disturbances,
Is it unnecessary in the design of this circuit or inadvertently omitted.
If so is there any harm in me adding it.

Thnx.
Haxxx
 

Attachments

Last edited:

audioguru

Well-Known Member
Most Helpful Member
The datasheet for the 555 and for the TSOP show a supply bypass capacitor. The TSOP is fed through a resistor.

The TSOP reduces its gain if you send it continuous pulses. Then its range is reduced. The datasheet shows bursts of pulses then a pause before the next burst of pulses to keep the gain high.
 

haxxx

New Member
I'm pretty sure i didn't understand one word u wrote.
Also i was asking about the capacitors in the circuits i attached.
 

audioguru

Well-Known Member
Most Helpful Member
I'm pretty sure i didn't understand one word u wrote.
I speak and read Electronics Technical english. which language do you speak and read?
I repeated the important details in the datasheets for the ICs.

(quote)Also i was asking about the capacitors in the circuits i attached.
Didn't you ask about your missing supply bypass capacitors that are talked about and shown in the datasheets?
The capacitors in your receiver circuit are not needed. The output is digital. Low when it receives a signal and high when it doesn't. The 100k resistor is not needed since the TSOP already has a resistor at its output.

The datasheet for the TSOP IR receiver shows that its automatic-gain-control reduces the gain when continuous IR is received because it might be interference from a compact fluorescent light bulb. The TSOP is designed for remote controls that have bursts of data separated with pauses then the TSOP keeps its gain high so that it is very sensitive.

It is all in the datasheets so you should read them.
 

haxxx

New Member
Thanks for your input, I appreciate it, u tech guys really have a short fuse.
I've never been in a class i just keep reading online.
slowly figuring out data sheets.
Much thanks to Colin55 and especially to Roff
who i started on a bad foot with but who has been very helpful.
If i understand u correctly and based on the graph in the datasheet, the
555 delivers the square wave output with necessary
pauses so the tsop can distinguish its signals from ambient light, my question is, wouldn't the resulting high and low output cycle from the tsop equal a false trigger to to the transistor, clearly it doesn't i just want to know why.

Regards,
Haxxx.
 

audioguru

Well-Known Member
Most Helpful Member
u tech guys really have a short fuse.
Sorry, but we get millions of demands from foreign students for us to do their homework for them. Their teachers are asleep.

If i understand u correctly and based on the graph in the datasheet, the 555 delivers the square wave output with necessary
pauses so the tsop can distinguish its signals from ambient light, my question is, wouldn't the resulting high and low output cycle from the tsop equal a false trigger to to the transistor, clearly it doesn't i just want to know why.
No.
The 555 delivers a continuous 36kHz signal exactly like a compact fluorescent light bulb which is interference. The TSOP has automatic gain control that expects bursts of remote control data for the gain to remain high. When continuous 36kHz IR puses are detected then it reduces its gain which reduces its range so that the interference is reduced.
You need a second 555 to turn the 36kHz one on and off like bursts of data for the gain and range to remain high.

You need to filter out the bursts in your application.
 

haxxx

New Member
Are you saying, as the circuit is, it won't reliably do what it was designed to do, essentially a low off the collector when the beam is interrupted.

P.S.
I did 11 years in the lab of an alumina plant,
I don't mind being a student again though.

Thanx again.
 

audioguru

Well-Known Member
Most Helpful Member
Are you saying, as the circuit is, it won't reliably do what it was designed to do, essentially a low off the collector when the beam is interrupted.
It will, but its gain will be reduced then its range will also be reduced.

It needs the 100 ohm resistor and 4.7uF as I showed and as shown in its datasheet.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top