ljille
Member level 2
This could seem basic, but I have trouble with an LM311 and TTL, please see ‘LM311_y_Shmitt.png’ to see diagram
With a LM311 comparator I’ve got a squared signal from a ICL8038 sinus signal, the squared very adequate to which I expected. It has some noise that I’d like not to have so I tried with some low pass filters but trying different values they lowered the signal into unwanted levels, so I thought that this noise was not so harmful. See ‘Salida_LM311.png’, where I’ve got 5.7V, a little bigger than TTL standard.
This signal is given to a shmitt trigger, 74LS14 (I have tried several chips of same number) but I had not an out signal. I looked for feeding or another possible mistakes, but I didn’t find any. As I know this component should give me a TTL standard, denied signal, but it gives me a plain low signal. See 'Salida_shmitt.png’. As this out is denied respect 'in' signal, it would be recognized as positive or high, still when high level of noise is lower than 0.5 V.
Then I tried putting the signal to an AND not inverting gate 74LS08 together with a squared 5V signal, but even when I have both high levels in some periods seen in the osciloscope (frequency of squared signal is 60 Hz), my result out of this gate is nothing.
Then I think:
Is there another requisite to interface an LM311 out to a TTL device that I am missing?
Do you see something in schematic who can avoid it to work? What am I missing?
I cutted one of the pull up resistances of 1Kohms connected to 5V to eliminate the case in which this would be influencing on the signal, but it only reduce amplitude of out signal of the LM311, while result in next stage is the same.
Do somebody see some way to make it work?
Thank you, very much
Luis Jiménez
With a LM311 comparator I’ve got a squared signal from a ICL8038 sinus signal, the squared very adequate to which I expected. It has some noise that I’d like not to have so I tried with some low pass filters but trying different values they lowered the signal into unwanted levels, so I thought that this noise was not so harmful. See ‘Salida_LM311.png’, where I’ve got 5.7V, a little bigger than TTL standard.
This signal is given to a shmitt trigger, 74LS14 (I have tried several chips of same number) but I had not an out signal. I looked for feeding or another possible mistakes, but I didn’t find any. As I know this component should give me a TTL standard, denied signal, but it gives me a plain low signal. See 'Salida_shmitt.png’. As this out is denied respect 'in' signal, it would be recognized as positive or high, still when high level of noise is lower than 0.5 V.
Then I tried putting the signal to an AND not inverting gate 74LS08 together with a squared 5V signal, but even when I have both high levels in some periods seen in the osciloscope (frequency of squared signal is 60 Hz), my result out of this gate is nothing.
Then I think:
Is there another requisite to interface an LM311 out to a TTL device that I am missing?
Do you see something in schematic who can avoid it to work? What am I missing?
I cutted one of the pull up resistances of 1Kohms connected to 5V to eliminate the case in which this would be influencing on the signal, but it only reduce amplitude of out signal of the LM311, while result in next stage is the same.
Do somebody see some way to make it work?
Thank you, very much
Luis Jiménez
