semiconductor
New Member
Some questions related to LM567 (tone decoder)
I'm working on a project. My duty is that: I have to detect a signal radiated from an IR LEDs. I use the SFH506 to demodulate the modulated signal (carrier frequency is 40kHz). I know the information frequency, it is: 40 Hz. I have to detect this frequency.
My tutor said that, I should use the IC LM567 to detect this frequency. When this frequency signal is applied to PIN 3, the output PIN 8 will be at LOW (other cases, PIN 8 always be HIGH).
When I carried out the experiment. I've got some problems.
- central frequency of LM567 is defied by R which is connected between PIN 6 and GND and C which is connected between PIN 6 and PIN 5. I chose R and C so that, the central frequency is 40 Hz (fo=1.1RC). Besides, I put between PIN 2 and GND a capacitor
- I decided to try this case: links PIN 5 (pulses with duty cycle is 50% and f = fo) to PIN 3 (input). I hope that PIN 8 will change its state (from HIGH to LOW). But it's not the case. I use oscilloscope to display pulse shape at PIN 8 when I apply the link between PIN 5 and PIN 3, first, the pulse shape on oscilloscope appears, then the duty cycle of this pulse decreases so after about 10 seconds, it's GND (Voltage at PIN 8 equals to 0). When I remove this links, the LOW state of PIN 8 maintains and after 10 minutes observing, this state does not change.
- first, I don't know why? I think, when there's no signal at the input PIN, the output PIN must be HIGH (not LOW forever).
- second, does LM567 operate as I said before? that is: when there's a signal with frequence within its bandpass (fo +/- num), output PIN will be LOW and be HIGH again vice versa (opposite case).
- Last, Can some one recommend me some other solutions to my problem (detect a fixed frequency signal)?
My due date is coming soon and I really need your helps
thank in advance!
Binh, From Vietnam.
I'm working on a project. My duty is that: I have to detect a signal radiated from an IR LEDs. I use the SFH506 to demodulate the modulated signal (carrier frequency is 40kHz). I know the information frequency, it is: 40 Hz. I have to detect this frequency.
My tutor said that, I should use the IC LM567 to detect this frequency. When this frequency signal is applied to PIN 3, the output PIN 8 will be at LOW (other cases, PIN 8 always be HIGH).
When I carried out the experiment. I've got some problems.
- central frequency of LM567 is defied by R which is connected between PIN 6 and GND and C which is connected between PIN 6 and PIN 5. I chose R and C so that, the central frequency is 40 Hz (fo=1.1RC). Besides, I put between PIN 2 and GND a capacitor
- I decided to try this case: links PIN 5 (pulses with duty cycle is 50% and f = fo) to PIN 3 (input). I hope that PIN 8 will change its state (from HIGH to LOW). But it's not the case. I use oscilloscope to display pulse shape at PIN 8 when I apply the link between PIN 5 and PIN 3, first, the pulse shape on oscilloscope appears, then the duty cycle of this pulse decreases so after about 10 seconds, it's GND (Voltage at PIN 8 equals to 0). When I remove this links, the LOW state of PIN 8 maintains and after 10 minutes observing, this state does not change.
- first, I don't know why? I think, when there's no signal at the input PIN, the output PIN must be HIGH (not LOW forever).
- second, does LM567 operate as I said before? that is: when there's a signal with frequence within its bandpass (fo +/- num), output PIN will be LOW and be HIGH again vice versa (opposite case).
- Last, Can some one recommend me some other solutions to my problem (detect a fixed frequency signal)?
My due date is coming soon and I really need your helps
thank in advance!
Binh, From Vietnam.