Placing diodes...

[shezza84]

Do I need a diode after the PIR sensors to stop voltage from entering the PIR switch backwards? In the schematic, of course one of the diodes Im asking about would be flipped horizontally...

If I do, will I have 2.4v dropped by the diodes alone? Do I need to have higher than 12v powering the circuit to make up for the voltage loss being the LEDs run off 12v roughly... or is this loss only beyond each diode? Does every diode drop voltage? Or only the ones blocking the voltage? If someone could simplify it a bit, would really appreciate it!

**broken link removed**

 

[ChrisP58]

Diodes will only have a voltage drop when they are forward biased. When they are blocking (reversed bias) there is no current flowing, so there is no voltage drop.

As to whether you need such protection, I can't see how you could have reverse current flowing. But I also don't know why you have a connection between your two lamps.

What are you trying to do?

 

[shezza84]

Ah, so current flowing through the diode = voltage drop. Got you!
Well rather than having each set of lights illuminated by each PIR sensor, I wanted the left one to turn on all the lights when a person enters and the right PIR sensor to turn all the lights on when the person exits. If it helps you understand a bit better, "Lamp 1" is the lights going through the garage and then "Lamp 2" is lighting going on the bottom rung of the fence to light up the garden and entry path. I lowered the wire to help me understand its the lower lighting...
There is probably going to be a PWM controller in there too on a side note.

Or is there a totally different way I should be doing this?

 

[alec_t]

You seem to be trying to power the LEDs directly from the PIR outputs. Have you made sure those outputs have the correct current and voltage ratings to drive the LEDs?

 

[shezza84]

Yes, the Photosensitive switch, PIR switch and PWM are all rated to handle the load I plan to put on them.

 

[audioguru]

If you are using LEDs then why are there incandescent light bulbs on your schematic??
Why do your incandescent light bulbs have 3 wires??

Your circuit is missing something to keep the lights turned on. The way it is shown on your schematic the lights will simply blink for a moment when someone walks past the PIR. But maybe your PIR sensors have a time delay to stay on for a minute?

 

[shezza84]

So the incandescent bulbs rather than LEDs is me being a schematic noob...
The 3 wires... Well its wires coming in and wires continuing to the next set of LEDs. So in actuality, I have an earth and positive wire going to each strip of LEDs.
Yes yes, it has a delay timer. Able to be set anywhere from 15 seconds to 8 minutes.

So do I need a diode to stop reverse voltage to the PIR switch?

 

[alec_t]

So do I need a diode to stop reverse voltage to the PIR switch?

We'd need to know the PIR output spec before we could answer that. Can you provide a link to its datasheet?

 

[shezza84]

This is as close as youll come to a datasheet Im guessing

• Model: TDL-2012-DC
• Working Voltage: 8-30VDC
• Load: 40A
• Working temperature:-20 °C ～ +50 °C
• Load capacity: LED lighting (for constant voltage/constant current LED light)
• Sensor angle: Cone angle of 140 degrees
• Induction distance:7-10m
• Time extension: 5~480s ± 30%(Switch can be set up)
• Size (L*W*H): 5.8 x 4.2 x 1.3cm/2.28"x1.65"x0.51"(approx)
• Color: White
• Quantity: 1 pc

 

[alec_t]

It's unclear from the PIR spec whether the output is via a relay or not. Safest, then, to use diodes to avoid possible conflict between the two PIRs.

 

[shezza84]

Oh I found a pic that shows it without the cover and it is via a relay

 

[alec_t]

Can we see the pic?

 

[shezza84]

Ok, I was mistaken... That wasnt the one. So if it is transistor switched, reverse voltage is ok? I recall reading somewhere that a relay without a diode doesnt like reverse voltage.
Anyway, the model is tdl-2012dc

 

[alec_t]

The diodes in your circuit are nothing to do with 'a relay without a diode'; they are to prevent one PIR trying to drive the other PIR.

 

[shezza84]

Oh I see!!! Though if the sensor isnt triggered, it will be open and no current would pass Id expect? Either way, if thats all Im looking out for, I can test it come the time

 

[alec_t]

Though if the sensor isnt triggered, it will be open and no current would pass Id expect?

That's one possibility. Another possibility (less likely IMO) is that the PIR output is a push-pull arrangement which pulls the output low when not triggered. That could well be fried if driven by a high output from another PIR.

 

[shezza84]

I guess for $5, I could take the risk to try and save a Volt.