View Full Version : [Question(s)] Need help building this circuit on a breadboard

02-07-2010, 11:17 AM
Closed. Reopened on new thread on 2/5/11.

02-07-2010, 11:31 AM
I'm not sure how someone can help you read a schematic through a post. All I can say is check your connections. Did you wire the op amp to V+ (pin 8) to 5V and V- (pin 4) to ground? These connections are assumed in the schematic. Other than that the schematic is straight forward.

Do you have a scope or mutimeter?

02-07-2010, 12:23 PM
The op amp is setup in differential gain mode.
Starting at the upper left corner:

5V to 68K R to [one side - 100 POT - other side] to ground
POT wiper (middle pin) to LM324 pin 2

5V to LDR to 3.9K R to ground
Connect a wire between the LDR and 3.9K R to LM324 pin3

LM324 pin3 to 1M R to LM324 pin1

LM324 pin1 to 1.5K R to [LED anode (long led) - LED cathode (flat side)] to ground

LM324 pin1 to load

LM324 pin 8 to 5V
LM324 pin 4 to ground

02-07-2010, 07:45 PM
[Curious] What was the problem?

02-08-2010, 05:47 PM
I was trying real hard to read your mind but you must be very far from my location.

Do you have a model number for the "bar LED"?

02-08-2010, 05:58 PM
I kinda figured it was a "Bar of LEDs" but you never can tell what ya get on these forums. Anyway, the LEDs work the same way as before only you don't have a flat side and a long lead. Instead you have a cathode (+) and anode (-). You had that before too but... you get the idea.