How to read this component as an input.

http://www.high-voltage-lab.com/105/economy-radar-detector

I currently have this radar built. I have it connect to A0 on the arduino. Do I have to add something so the arduino can read it as an input?

You could use a digital pin. The output to the piezo is either LOW (near 0 volts) or HIGH (near 9 volts). The second section of the 1458 is used as a comparator.

I assume you are planning to measure where they have the buzzer (that's where you should measure).

Remove the buzzer. Tie arduino ground to detector ground. I'd then try connecting a diode to the output of the opamp (where the buzzer was) with the band towards the opamp, other end to Arduino IO pin. That way, when radar is detected, it'll pull the pin low, but when it's not (and thus the voltage is up around positive supply voltage), the diode will keep the voltage from going above the arduino supply voltage. OR - use two resistors of the same value (say, 10k) in series between opamp output and ground, with arduino pin connected in middle - thus, if output is high, the arduino input is half that, which is still high as far as the arduino is concerned (half of close to 9v), and if it's low, the pin will go low as well. IO pin wants to be INPUT_PULLUP with the diode scheme, INPUT with the voltage divider. You don't need an analog pin - it's on/off.

Do not connect the output of the opamp directly to the Arduino, as it can be higher than 5v (not sure how close to the rails those opamps get with 9v supply, but I suspect it's more than 5v)

The tuning method used there is atrocious, and the design is ancient.

Modern radar guns are more sophisticated; many of them no longer use the same old radar bands, and lasers are getting more common.

SurferTim: You could use a digital pin. The output to the piezo is either LOW (near 0 volts) or HIGH (near 9 volts). The second section of the 1458 is used as a comparator.

If I dont add the piezo can I add a resistor to do the job?

To do what job?

DrAzzy: To do what job?

I attached a diode but the voltage that i get through it's output ranges from 2.0-2.2 what can i do?

Do you have the pin it's connected to set at INPUT_PULLUP? And you have grounds connected?

Also, please measure the voltages on the output pin when it's not detecting any radar.

DrAzzy:
Do you have the pin it’s connected to set at INPUT_PULLUP? And you have grounds connected?

Also, please measure the voltages on the output pin when it’s not detecting any radar.

I did not have it grounded. The problem now is that it always reads a 1.

When it should be detecting radar (ie, there's a source of radar), what's the voltage on both sides of the diode?

It should output a 1 when there's no radar, and go low when there is - do you know that the detector is actually working?

If the voltage coming out of the opamp doesn't change when radar is detected, then the problem is the detector.

DrAzzy: When it should be detecting radar (ie, there's a source of radar), what's the voltage on both sides of the diode?

It should output a 1 when there's no radar, and go low when there is - do you know that the detector is actually working?

If the voltage coming out of the opamp doesn't change when radar is detected, then the problem is the detector.

When i change my potentiometer from low to high it switches voltage over the diode to 2.0v-2.3v.

Jellyroll135: When i change my potentiometer from low to high it switches voltage over the diode to 2.0v-2.3v.

DrAzzy: When it should be detecting radar (ie, there's a source of radar), what's the voltage on both sides of the diode?

It should output a 1 when there's no radar, and go low when there is - do you know that the detector is actually working?

If the voltage coming out of the opamp doesn't change when radar is detected, then the problem is the detector.

i got it to work! I have 1 more question about this though. When i try to add an external power supply the diode over heats when i ground it to the arduino. How do i fix this? I believe it is short circuited somewhere but i dont see it.

Hi,

Can you please post a copy of how you have the detector connected to the arduino and where you have placed the diode. CAD or a picture of a hand drawn circuit in jpg, png?

Tom.... :)

http://www.high-voltage-lab.com/105/economy-radar-detector

There is some interesting stuff at that website you linked there. One of their projects is for a very simple coil gun. One that won't work very well at all. It was designed by Rev. Thomas Scarborough.

The end of the description is interesting, however. The final sentence says "In a forthcoming edition of EPE, the author will describe how readers may land a small projectile on Mars. "

TomGeorge:
Hi,

Can you please post a copy of how you have the detector connected to the arduino and where you have placed the diode.
CAD or a picture of a hand drawn circuit in jpg, png?

Tom… :slight_smile:

Sorry it took me so long to get back to you. This is the basic idea I hope it makes sense.Seems like a simple fix but i cant figure it out. The voltage over the resistor is 1.1v -2.7v.

Hi, Where is your diode? What is the power supply you are using, and where are you connecting it to the arduino?

Tom.... :)

Has anyone managed to detect a radar gun with that circuit? I very much doubt it.

Russell.