7555 timer board

Bernard

Joined Aug 7, 2008
5,784
The traces are hard to see, but I think this is what it looks like, if you add connection from pin 7 to top of R1. Only the bare minimum was etched away, so component side is + battery & back is - battery. Might be a clip to hold CR2032 battery inplace.
 

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THE_RB

Joined Feb 11, 2008
5,438
If Bernard's diagram accurately represents the PCB it will not work because the sensing sytsem is complete (pins 2 and 6) but there is no discharge mechanism for the timing cap C1.

Normally there would be a connection from between the two resistors (VR1 and R1) to the discharge pin 7.
:)

It is also a good idea to put a small resistor (220 ohm) between the top of Vr1 and the + power pin. That protects from overcurrent fault if the pot VR1 is turned to zero ohms.
 

ScottWang

Joined Aug 23, 2012
7,397
The traces are hard to see, but I think this is what it looks like, if you add connection from pin 7 to top of R1. Only the bare minimum was etched away, so component side is + battery & back is - battery. Might be a clip to hold CR2032 battery inplace.
The common point of VR1 and R1 already were connected to the pin 7.
 

ScottWang

Joined Aug 23, 2012
7,397
Upload the schematic to the forum.
If you mean that it doesn't work is the LED didn't flash, you should check the LED first, and the value of R2, and measure all the wires.
 

Bernard

Joined Aug 7, 2008
5,784
One question I have, are the ground connections of C1, pin 1, & LED plated thru holes or soldered in jumpers. As THE_RB pointed out, a resistor in series with VR1 would be adviseable, or it might already be part of VR1.
 

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tresguey

Joined Apr 22, 2013
55
Here is the schematic from KiCad


View attachment Blinky.sch


The ground connections are plated through holes to ground on the back side of the board.

The LED does work I did de-solder and checked it. When the battery is placed in the circuit it gets drained quick.
 
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ScottWang

Joined Aug 23, 2012
7,397
Vcc to Pin 7 can use 1K, R1 can be replace by a 10K+VR500K, 100K+VR500K or 220K + VR500K, or 470K+VR100K, etc..., it depends on how large the range you like to adjust.
 
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