14-11-2016, 09:53 PM
(This post was last modified: 14-11-2016, 09:54 PM by Geordie McBoyne.)
Hi Trevor,
I notice that you have supplied the output from the LM1881 to pin 5 of the 555 timer. Pin 5 is connected directly to the three resistor potential divider network in the IC. I'm not sure if this is the correct pin for sync purposes, In the past I have used the reset pin 4 as a sync pulse injection point.
Normally pin 5 is connected to a decoupling capacitor of say 0.1microfarards. Pin 4 is normally connected to the VCC pin. A high to low transition resets the timer.
The LM1881: pin 3 is the vertical sync output. I assume that the pin goes low only during the vertical sync period, that is during the broad pulse train and not including the equalising pulse periods. The timing chart indicates that this is so.
I'm thinking if the V pulse from pin 3 of the LM1881 goes from VCC to ground this could be supplied to the reset pin of the 555.
Geordie McBoyne.
I notice that you have supplied the output from the LM1881 to pin 5 of the 555 timer. Pin 5 is connected directly to the three resistor potential divider network in the IC. I'm not sure if this is the correct pin for sync purposes, In the past I have used the reset pin 4 as a sync pulse injection point.
Normally pin 5 is connected to a decoupling capacitor of say 0.1microfarards. Pin 4 is normally connected to the VCC pin. A high to low transition resets the timer.
The LM1881: pin 3 is the vertical sync output. I assume that the pin goes low only during the vertical sync period, that is during the broad pulse train and not including the equalising pulse periods. The timing chart indicates that this is so.
I'm thinking if the V pulse from pin 3 of the LM1881 goes from VCC to ground this could be supplied to the reset pin of the 555.
Geordie McBoyne.
