Help with high level circuit analysis (ie, how's this work)

[ADWSystems]

I purchased a Velleman kit K3502 Ultrasonic Parking Radar. I have no intention of ever using it on my car, but I may be able to use it as a level detector; a bin full sensor to be exact. I'd like to know a little more about how it is put together before I try to make it work for my application.

I have tried to simulate the circuit but since I don't know what the waveform to/from the sensors looks like I don't think the simulation is producing a good approximation .

I have attached the schematic and marked areas that I was able to identify their function. But there are several other connections and areas that I have been able to wrap my head around, so any assistance would be appreciated.

1. What is the purpose of the CD4068 (8In NAND/AND)tied to the CD4020 (14 stage ripple counter)?
2. Why is transmitter drive dependent on CD4060 Q7 and CD4068 AND output?
3. How does the sensitivity adjust circuit work (top just right of center)? The receiver input (/RW bottom center) is connected via a diode to a NAND latch (upper right). How does RV1 effect the sensitivity if /RW is in between two logic gates?
4. What function is built at the bottom center of the page with A1 and T1 included? Auto-gain adjust?

 

[Diver300]

The crystal frequency isn't shown. I'm guessing 10 MHz and my answers are based on that.
1. The output of the CD4068 will be on for a very small fraction of the time. About 0.1 ms every 25 ms. That will initiate the pulses of sound.
2. CD4060 Q7 oscillates at 78 kHz. The transmitter drive is therefore 78 kHz for about 0.1 ms every 25 ms.
3. While the pulse is happening, C3 charges up via D1. After the pulse finishes, C3 discharges via RV1 and R2. Once that voltage is low enough, the output on N1 will stop the N2/N3 latch operating. So RV1 varies the maximum time, and therefore the maximum distance, at which an object can be sensed.
4. A1 is an amplifier to create a mid-rail voltage, so that the other amplifiers can have a positive or negative signal compared to the mid voltage.
T1 is to turn off the receiver while the transmit pulse is happening.

 

[ADWSystems]

I get the mid-rail voltage piece (#4) and the use of T1.

Let me see if I understand #3. RV1 controls the discharge time such that the slower C3 discharges, the more time there is for the sensor to detect an object; right? ie., more time for /RW to go low? If /RW does low before C3 is discharged, the latch fires.

Won't the buzzer automatically reset when IC2 Q4-Q11 all go high? So if the object remains present, the buzzer will turn on and off (the NAND latch will keep setting and resetting).

I'm still curious as to what purpose NANDing (is that word?) IC1 Q7 with IC2 Q4-Q11 ANDed serves.

I also see a similar charge/discharge structure using C4 and NAND of IC2 Q4-Q11. What is the purpose of the section?

 

[Diver300]

Won't the buzzer automatically reset when IC2 Q4-Q11 all go high? So if the object remains present, the buzzer will turn on and off (the NAND latch will keep setting and resetting).

Yes, it will keep turning on and off. That will probably be audible, but the important thing is that if there is an object present, there is some sound.

 

[Diver300]

I'm still curious as to what purpose NANDing (is that word?) IC1 Q7 with IC2 Q4-Q11 ANDed serves.

If you connected the sounder to IC1 of Q7 directly, there would be a constant 78 kHz signal. There would be no gaps which the receiver could work in.

If you connected the sounder to the ANDed combination of IC2 Q4-Q11, all you would get is a series of clicks. There would not be enough energy transmitted to trigger the receiver.

By having both the signals ANDed together, there are short bursts of sound.

 

[Diver300]

I also see a similar charge/discharge structure using C4 and NAND of IC2 Q4-Q11. What is the purpose of the section?

That is to force a minimum detection distance/time. It is to make sure that the transmitted signal has died down before detection starts.

 

[ADWSystems]

Thank you for your help. I don't think I could have come up with this circuit if I had tried.

I understand but don't, that IC1/IC2 NAND gate thing. I think the next step is to assemble the kit and try it out. I am hoping that it will be able to detect when the bin is full for the chip collector for my woodworking tools. I have two things that concern me and neither can be determined from circuit analysis. I hope it can detect the chips in the first place. Secondly, I hope there is enough dampening that the chips flying around while the fan is running doesn't set it off. I guess we'll see.

 

[keykeybro]

The crystal frequency isn't shown. I'm guessing 10 MHz and my answers are based on that.
1. The output of the CD4068 will be on for a very small fraction of the time. About 0.1 ms every 25 ms. That will initiate the pulses of sound.
2. CD4060 Q7 oscillates at 78 kHz. The transmitter drive is therefore 78 kHz for about 0.1 ms every 25 ms.
3. While the pulse is happening, C3 charges up via D1. After the pulse finishes, C3 discharges via RV1 and R2. Once that voltage is low enough, the output on N1 will stop the N2/N3 latch operating. So RV1 varies the maximum time, and therefore the maximum distance, at which an object can be sensed.
4. A1 is an amplifier to create a mid-rail voltage, so that the other amplifiers can have a positive or negative signal compared to the mid voltage.
T1 is to turn off the receiver while the transmit pulse is happening.

I know, I'm bring up the old thread, but I can't understand why CD4060 Q7 oscillates at 78kHZ. Isn't there 40kHz, because of 5MHz/2^7=50000000/128=40kHz???

 

[ADWSystems]

Where did you get 5MHz? Using 10Mhz in your formula, you would get 80kHz

 

[keykeybro]

Ou, I'm sorry, the right frequency of the quartz crystal is 5MHz. You couldn't know it. I'm sorry