Build Car Blind Spot Detection Whit CDM324 - Page 1
Forum section: electronics / rf-microwave

author: soodi1100
author_rank: Newbie
timestamp: February 01, 2020, 10:18:16 am
content: HiI am an Iranian studentI want to Build Car Blind Spot Detection radar with a cdm324 sensorI connected the sensor to the attached schematicI count the MAX9031 output with the microcontrollerBut the output changes both as the object moves away and the object approaches.However, radar should only detect the approach of the object and objects such as trees or roads or .... (other than cars) should not be detected.How to read the sensor output in order to use this sensor for Car Blind Spot Detection؟what is your opinion?Thanks

author: Miti
author_rank: Super Contributor
timestamp: February 02, 2020, 03:41:00 pm
content: You’ll have to detect the change direction in the IF amplitude. Moving towards you will go from low to high, away from you from high to low. Check this out:https://youtu.be/9WiJJgIi3W0You need a different sensor for easier directional detection.

author: soodi1100
author_rank: Newbie
timestamp: February 02, 2020, 08:05:49 pm
content: Thank you so muchDue to limitations like high price or lack of sensor, I had to use the CDM324 and also because of the limited angle (Horizontal: Typ.80° Vertical:Typ.32°)which is suitable for making blind spot detection.How to Detect IF Range Change from low to high?What schematic or method do you suggest?thank

author: Miti
author_rank: Super Contributor
timestamp: February 05, 2020, 03:46:55 am
content: I don't know much about the technology behind the blind spot detection but I think your approach is wrong. You say "But the output changes both as the object moves away and the object approaches." What about the objects that move at the same speed? Doppler detects only moving objects but you would want to know when an object is in your blind spot even if it doesn't move relative to you. Am I missing something?

author: Berni
author_rank: Super Contributor
timestamp: February 05, 2020, 06:30:01 am
content: What you need is a radar module with quadrature output.Those radars have two mixers inside of them that are fed a 90 degree out of phase LO signal so the resulting two IF is also shifted by 90 degrees. So if one signal is leading forwards by 90 degrees or lagging behind 90 degrees determines the direction of the target (Because it is producing a positive or negative doppler shift on the signal)Normal doppler radar can also only see objects moving reasonably fast. If you want to see slow moving or stationary objects then you also need to have FM modulation capability in the radars local oscillator. This modulation causes the number of wavelengths between antenna and target to change constantly so that they also produce a signal.Radar is simple in principle but can quickly get a lot more complicated in order to make it work well in certain real world use cases.

author: soodi1100
author_rank: Newbie
timestamp: February 05, 2020, 12:41:47 pm
content: Quote from: Miti on February 05, 2020, 03:46:55 amThis system should detect cars approaching your vehicleBut it should not detect the road or objects around the road that are moving away from your car

author: soodi1100
author_rank: Newbie
timestamp: February 05, 2020, 01:04:45 pm
content: Quote from: Berni on February 05, 2020, 06:30:01 amThis is part of the CDM324 specification:This particular radar sensor outputs a quadrature signal, basically you get a sine and a cosine-like wave from the I and Q outputs, with a relatively large static offset. The mutual phase between these signals allows you to tell if an object is moving toward or away from the sensor. In a complex frequency spectrum this appears as either a positive or negative frequency.__________________________________________It is used in blind spot detection systems :https://www.aliexpress.com/item/4000012550318.htmlIs it made of a combination of two sensors?Can the combination of two CDM324 be used?Are you introducing a low price sensor?Thanks

author: Berni
author_rank: Super Contributor
timestamp: February 05, 2020, 04:57:46 pm
content: Yep that alibaba link is the kind of radar module you need. It has the I and Q outputs.No you can't use two separate modules because they must be both run from the same local oscillator so that both mixers stay 90 degrees out of phase.

author: soodi1100
author_rank: Newbie
timestamp: February 05, 2020, 07:20:04 pm
content: Quote from: Berni on February 05, 2020, 04:57:46 pmThank youLink is missingPlease give the purchase link

author: Berni
author_rank: Super Contributor
timestamp: February 05, 2020, 09:02:17 pm
content: Quote from: soodi1100 on February 05, 2020, 01:04:45 pmYou posted the link there!