Schematic for Cycle Sentry: 24-GHz Radar For Bicyclist Detection:...

Radar Test Board Overview

flux

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General

Project

BOM

Knowledge Base

Using Knowledge Base Tool.

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Here is a concise, system-level explanation of the project, using what’s in your schematic and BOM.

Purpose

A 24 GHz CW/FMCW radar test board that transmits and receives at 24 GHz, brings baseband I/Q (in-phase and quadrature) down to analog IF, conditions it with selectable gains, and digitizes/controls it with a microcontroller. It also exposes RF via SMA for lab instruments and uses an automotive 12 V input with on-board 5 V and 3.3 V rails.

Core components and how they interact

Table

Block	Designators	Role	Key connections
24 GHz radar transceiver	U3	RF front end with TX, RX, baseband I/Q outputs, tuning input	TX↔J4 (ANT_TX), RX↔J5 (ANT_RX), IFI/IFQ → U2, V_TUNE ← U6 output
IF/baseband conditioning	U2	Quad op-amp stages for IFI/IFQ: gain, buffering, filtering	IFI/IFQ from U3; outputs to MCU analog pins and/or switches
Gain/path selection	U7, U8	Dual bilateral analog switches to gate/multiplex high/low‑gain I/Q paths	Switches steer Out_IL/Out_QL/O_IH/O_QH from U2 to the MCU and test points
MCU and control	U4	Sampling IF channels, SPI/JTAG/I2C connectivity, DAC_PWM for VCO tune	ADC inputs on PA5/PA6, PWM DAC on PB4 → V_TUNE chain; JTAG via J1; SPI via J2; I2C via J3; clock via Y1
PWM-to-DC tune chain	R30, R31, C25, C26, U6	Two-stage RC low-pass and op-amp buffer to convert MCU PWM into a stable V_TUNE for U3	DAC_PWM → RC1 → RC2 → U6 → FREQ_TUNE net → U3
Power: 12 V in, 5 V, 3.3 V rails	D1, U1, U5, bulk caps C1/C22/C23	Reverse-polarity + surge headroom, 12 V → 5 V regulation, then 5 V → 3.3 V for RF/MMCU	12V → D1 → U1 (5 V) → U5 (3.3 V)
RF interfaces	J4, J5	50 Ω SMA end-launch for TX/RX to instruments/antennas	Direct to U3 TX/RX pins
Debug/program	J1, J2, J3, clock Y1	JTAG, SPI header, I2C header; stable MCU clock	JTAG TMS/TCK/TDI/TDO, SPI MOSI/MISO/SCK, I2C SDA/SCL; XTAL1/2 nets to Y1

Design and implementation details

RF front end: U3 TX goes to J4 and RX to J5. Baseband IF nets IFI and IFQ leave U3 and feed the multi-stage analog chain in U2.
IF signal conditioning: U2 implements high‑/low‑gain paths and filtering for both I and Q, creating IFI_HG/LG and IFQ_HG/LG nets. Selection/gating is handled by the analog switches U7 and U8, which route the appropriate outputs toward the MCU inputs and/or measurement points.
Tuning control (VCO sweep/offset): The MCU’s PWM (DAC_PWM) is smoothed by cascaded RCs R30/C25 and R31/C26, then buffered by U6 to drive U3 V_TUNE (FREQ_TUNE net). This provides a DC‑accurate control voltage from a digital PWM source for CW/FMCW modes.
Processing and I/O: U4 reads analog IF channels (e.g., PA5/PA6), controls prescaler/divider signals, and exposes JTAG (J1), SPI (J2), and I2C (J3) for configuration and data.
Power tree: 12 V input is protected by D1. U1 generates 5 V (bulk reservoirs C1, C22), and U5 generates 3.3 V (reservoir C23) for the RF/MMCU domains.

Key technologies, dependencies, design choices, and trade-offs

24 GHz RF with SMA breakouts: End‑launch J4/J5 simplifies lab bring‑up and antenna swaps but requires impedance‑controlled launch and tight ground referencing to avoid mismatch and radiation.
Analog IF chain with selectable gain: Using U2 plus U7/U8 is flexible and low‑cost. Trade‑offs include switch on‑resistance/capacitance adding noise/bandwidth limits and the JFET‑op‑amp’s noise/offset/PSRR vs modern low‑noise, rail‑to‑rail alternatives.
PWM DAC for V_TUNE: The two‑stage RC plus U6 buffer is inexpensive and firmware‑simple. Trade‑offs are ripple/leakage, settling time, and temperature drift; the filter corner must balance ripple suppression with tuning agility for FMCW sweeps.
Power via cascaded LDOs: U1 → U5 is clean and RF‑friendly but thermally inefficient from 12 V. It’s robust for a bench/automotive test setting; thermal rise and load dump transients should be reviewed.
Testability: Breaking out RF and digital/programming headers (J1, J2, J3) accelerates bring‑up and iteration.

Potential challenges and performance considerations

24 GHz layout discipline: Launch geometry, reference plane continuity, solder mask control around J4/J5, and short RF paths to U3 are critical to avoid mismatch and parasitic radiation.
IF noise and dynamic range: Low‑frequency flicker noise, switch on‑resistance/capacitance, and op‑amp input noise set the floor. Ensure anti‑aliasing and bandwidth align with IF content and ADC sampling.
V_TUNE purity: Residual PWM ripple or long settling in the R30/R31/C25/C26 network can modulate the VCO, causing FM spurs and range/Doppler artifacts. Place these parts close to U6 and U3 with a clean analog ground.
Power integrity and EMI: The 12 V to 5 V drop in U1 and 5 V to 3.3 V in U5 dissipate heat; decoupling and bulk (C1, C22, C23) location matters for load steps (TX on/off).
Crosstalk/grounding: Close analog/digital domains and switchable paths can couple; partition grounds and route IF returns directly; minimize loop areas around U2, U7, U8.

Real-world applications

Blind‑spot bicyclist detection on parked cars, occupancy sensing, short‑range motion profiling, and lab validation of CW/FMCW algorithms using the SMA breakouts and MCU‑captured I/Q.

Suggestions for improvement and future enhancements

Signal chain
- Evaluate U2 stage noise/bandwidth vs your IF targets; consider consolidating gain control to minimize switch parasitics via fewer stages.
- Refine the PWM‑DAC filter (R30, R31, C25, C26) for spur suppression vs sweep agility; verify ripple at the V_TUNE pin of U3.
Power and robustness
- Review thermal headroom in U1/U5 at worst‑case input and load. Consider surge/load‑dump resilience at the 12 V entry ahead of D1.
Layout/EMC
- Tighten the RF launches around J4/J5; add keepouts and stitching vias as needed; keep U3 decoupling ultra‑local.
- Consider shielding can provisions over U3 and the IF chain.
System/firmware
- Add calibration routines (DC offset, I/Q imbalance, phase calibration vs temperature). Use the prescaler/divider output from U3 for sweep linearization feedback if applicable.
- Provide firmware hooks to switch U7/U8 paths during runtime for auto‑range.

If you’d like, I can review specific subcircuits—for example the PWM‑to‑V_TUNE filter or the IF op‑amp stages—and suggest concrete component values and placement guidelines.

Op amp search

LDO alternative

Power dissipation calc

RF layout guidelines

Ground partitioning advice

79 days

Ready.

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C15

Capacitance

15n F

C26

Capacitance

470n F

R13

Resistance

10k Ω

R15

Resistance

10k Ω

R17

Resistance

100k Ω

C27

Capacitance

0.1u F

C12

Capacitance

220u F

R14

Resistance

1k Ω

R21

Resistance

100k Ω

R24

Resistance

100k Ω

R30

Resistance

470 Ω

C11

Capacitance

15n F

C28

Capacitance

0.1u F

Capacitance

0.1u F

R10

Resistance

100k Ω

C17

Capacitance

2700p F

R18

Resistance

1k Ω

C18

Capacitance

220u F

R22

Resistance

3.3k Ω

R23

Resistance

33k Ω

Resistance

100k Ω

C13

Capacitance

5600p F

R31

Resistance

1k Ω

3V3

C14

Capacitance

220u F

R19

Resistance

10k Ω

Capacitance

5600p F

C19

Capacitance

5600p F

C25

Capacitance

1u F

R16

Resistance

33k Ω

2V5

O_QH

DAC V_follower

End of Life

Cap_IL

DAC_PWM

IFI_LG

O_IH

Out_IL

IFI_HG

Out_QL

Q_LSW

Cap_IH

IFQ Low Gain

Bypass for init charging

IFQ_LG

IFI High Gain

IFQ_HG

Cap_QL

Cap_QH

2V5

Cap_QL

Freq_Tune

Q_HSW

I_LSW

I_HSW

Cap_IH

O_IH

Cap_QH

Out_QL

IFQ

Reviews

Design Rule Checks

Overlapping Copper • 22

Des	Net	Des	Net
Trace 0b8e	ANT_TX	Pad:Pad	None
Trace 5e15	ANT_TX	Pad:Pad	None
U3:TX	ANT_TX	Pad:Pad	None
Trace 4a66	GND	U3:17	None
Trace 2541	GND	U3:17	None
Trace 5277	GND	U3:17	None
Pad:Pad	None	J5:1	ANT_RX
Pad:Pad	None	Trace 66b1	ANT_RX
Pad:Pad	None	Trace aaee	ANT_RX
Pad:Pad	None	U3:RX	ANT_RX
Pad:Pad	None	J4:1	ANT_TX
U3:17	None	Trace b1c3	GND
U3:17	None	Trace de38	GND
U3:17	None	Trace dff0	GND
U3:17	None	Trace ec75	GND
U5:1c4db151	None	Trace 5650	GND
U5:1c4db151	None	Trace c670	GND
U5:1c4db151	None	U5:GND	GND
U5:1c4db151	None	U5:GND	GND
U5:1c4db151	None	U5:GND	GND
U5:1c4db151	None	U5:GND	GND
U5:1c4db151	None	Via	GND

Invalid Layer

Reports nodes that are assigned to a layer that doesn't exist in the layout stackup.

Component Overrides • 41

	Designator	Ruleset
	Circle Shape	Override rule for Circle Shape
	Circle Shape	Override rule for Circle Shape
	D1:ANODE	Override rule for ANODE
	Fab Shapes	Override rule for Fab Shapes
	J1:VCC	Override rule for VCC
	R28:P2	Override rule for P2
	U4:VCC	Override rule for VCC
	U7:9	Override rule for 9
	U8:9	Override rule for 9
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rules for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	＊｀REF｀＊	Override rule for ＊｀REF｀＊
	AVR-JTAG-10	Override rule for AVR-JTAG-10
	C＊＊	Override rule for C＊＊
	C＊＊	Override rule for C＊＊
	C＊＊	Override rule for C＊＊
	GND	Override rule for GND
	GND	Override rule for GND
	Silk Shapes	Override rule for Silk Shapes
	Silk Shapes	Override rule for Silk Shapes
	SRST	Override rule for SRST
	TCK	Override rule for TCK
	TDI	Override rule for TDI
	TDO	Override rule for TDO
	TMS	Override rule for TMS
	TRST	Override rule for TRST
	VCC	Override rule for VCC
	VREF	Override rule for VREF

Airwires • 1

	Designators	Net
	D1:ANODE, J3:PIN_4	Net 10

Layers with Multiple Fills

Reports layers that have multiple copper fills of different nets. Make sure the Connected Layers rule value of nets with fills is valid.

Floating Copper • 5

	Name
	Via-3-6
	Trace 55dc, Trace b389
	Trace 0af0
	Trace 4eb6
	Trace 39ba

Protected Intrusions

Reports intrusions from objects of other nets into polygons or fills that have the Protected layout rule applied.

Missing Footprints

Reports components that need a footprint but don't have one.

Manufacturing

Manufacturer Part Number • 3

	Designator	MPN
	.1	None
	J3	None
	U3	None

Parts Available

Beta

Checks that all components are available from distributors.

System Checks

Auto-Layout

Beta

Reports issues with Auto-Layout if Flux cannot route something or must ignore a configuration.

Passive Components

Resistor Power Rating

Beta

Checks that the power traveling across a given resistor is under its rating with 50% headroom.

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Pull Up/Pull Down Presence

Beta

Checks that IC pins that require pull up or pull down resistors have them.

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Capacitor Voltage Rating

Beta

Checks that capacitors have appropriate voltage ratings to prevent overheating and ensure reliable circuit operation.

Ground
A common return path for electric current. Commonly known as ground.
jharwinbarrozo
20.5M
Net Portal
Wirelessly connects nets on schematic. Used to organize schematics and separate functional blocks. To wirelessly connect net portals, give them same designator. #portal
jharwinbarrozo
43.0M
Power Net Portal
Wirelessly connects power nets on schematic. Identical to the net portal, but with a power symbol. Used to organize schematics and separate functional blocks. To wirelessly connect power net portals, give them the same designator. #portal #power
jharwinbarrozo
11.4M
Generic Resistor
A generic fixed resistor for rapid developing circuit topology. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard resistor values: 1.0Ω 10Ω 100Ω 1.0kΩ 10kΩ 100kΩ 1.0MΩ 1.1Ω 11Ω 110Ω 1.1kΩ 11kΩ 110kΩ 1.1MΩ 1.2Ω 12Ω 120Ω 1.2kΩ 12kΩ 120kΩ 1.2MΩ 1.3Ω 13Ω 130Ω 1.3kΩ 13kΩ 130kΩ 1.3MΩ 1.5Ω 15Ω 150Ω 1.5kΩ 15kΩ 150kΩ 1.5MΩ 1.6Ω 16Ω 160Ω 1.6kΩ 16kΩ 160kΩ 1.6MΩ 1.8Ω 18Ω 180Ω 1.8KΩ 18kΩ 180kΩ 1.8MΩ 2.0Ω 20Ω 200Ω 2.0kΩ 20kΩ 200kΩ 2.0MΩ 2.2Ω 22Ω 220Ω 2.2kΩ 22kΩ 220kΩ 2.2MΩ 2.4Ω 24Ω 240Ω 2.4kΩ 24kΩ 240kΩ 2.4MΩ 2.7Ω 27Ω 270Ω 2.7kΩ 27kΩ 270kΩ 2.7MΩ 3.0Ω 30Ω 300Ω 3.0KΩ 30KΩ 300KΩ 3.0MΩ 3.3Ω 33Ω 330Ω 3.3kΩ 33kΩ 330kΩ 3.3MΩ 3.6Ω 36Ω 360Ω 3.6kΩ 36kΩ 360kΩ 3.6MΩ 3.9Ω 39Ω 390Ω 3.9kΩ 39kΩ 390kΩ 3.9MΩ 4.3Ω 43Ω 430Ω 4.3kΩ 43KΩ 430KΩ 4.3MΩ 4.7Ω 47Ω 470Ω 4.7kΩ 47kΩ 470kΩ 4.7MΩ 5.1Ω 51Ω 510Ω 5.1kΩ 51kΩ 510kΩ 5.1MΩ 5.6Ω 56Ω 560Ω 5.6kΩ 56kΩ 560kΩ 5.6MΩ 6.2Ω 62Ω 620Ω 6.2kΩ 62KΩ 620KΩ 6.2MΩ 6.8Ω 68Ω 680Ω 6.8kΩ 68kΩ 680kΩ 6.8MΩ 7.5Ω 75Ω 750Ω 7.5kΩ 75kΩ 750kΩ 7.5MΩ 8.2Ω 82Ω 820Ω 8.2kΩ 82kΩ 820kΩ 8.2MΩ 9.1Ω 91Ω 910Ω 9.1kΩ 91kΩ 910kΩ 9.1MΩ #generics #CommonPartsLibrary
jharwinbarrozo
1.5M
Generic Capacitor
A generic fixed capacitor ideal for rapid circuit topology development. You can choose between polarized and non-polarized types, its symbol and the footprint will automatically adapt based on your selection. Supported options include standard SMD sizes for ceramic capacitors (e.g., 0402, 0603, 0805), SMD sizes for aluminum electrolytic capacitors, and through-hole footprints for polarized capacitors. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard capacitor values: 1.0pF 10pF 100pF 1000pF 0.01uF 0.1uF 1.0uF 10uF 100uF 1000uF 10,000uF 1.1pF 11pF 110pF 1100pF 1.2pF 12pF 120pF 1200pF 1.3pF 13pF 130pF 1300pF 1.5pF 15pF 150pF 1500pF 0.015uF 0.15uF 1.5uF 15uF 150uF 1500uF 1.6pF 16pF 160pF 1600pF 1.8pF 18pF 180pF 1800pF 2.0pF 20pF 200pF 2000pF 2.2pF 22pF 20pF 2200pF 0.022uF 0.22uF 2.2uF 22uF 220uF 2200uF 2.4pF 24pF 240pF 2400pF 2.7pF 27pF 270pF 2700pF 3.0pF 30pF 300pF 3000pF 3.3pF 33pF 330pF 3300pF 0.033uF 0.33uF 3.3uF 33uF 330uF 3300uF 3.6pF 36pF 360pF 3600pF 3.9pF 39pF 390pF 3900pF 4.3pF 43pF 430pF 4300pF 4.7pF 47pF 470pF 4700pF 0.047uF 0.47uF 4.7uF 47uF 470uF 4700uF 5.1pF 51pF 510pF 5100pF 5.6pF 56pF 560pF 5600pF 6.2pF 62pF 620pF 6200pF 6.8pF 68pF 680pF 6800pF 0.068uF 0.68uF 6.8uF 68uF 680uF 6800uF 7.5pF 75pF 750pF 7500pF 8.2pF 82pF 820pF 8200pF 9.1pF 91pF 910pF 9100pF #generics #CommonPartsLibrary
jharwinbarrozo
1.5M
Generic Inductor
A generic fixed inductor for rapid developing circuit topology. *You can now change the footprint and 3D model at the top level anytime you want. This is the power of #generics
jharwinbarrozo
15.1k
Terminal
An electrical connector acting as reusable interface to a conductor and creating a point where external circuits can be connected.
natarius
RMCF0805JT47K0
47 kOhms ±5% 0.125W, 1/8W Chip Resistor 0805 (2012 Metric) Automotive AEC-Q200 Thick Film #forLedBlink
jharwinbarrozo
1.2M
875105359001
10uF Capacitor Aluminum Polymer 20% 16V SMD 5x5.3mm #forLedBlink #commonpartslibrary #capacitor #aluminumpolymer #radialcan
jharwinbarrozo
1.2M
CTL1206FYW1T
Yellow 595nm LED Indication - Discrete 1.7V 1206 (3216 Metric) #forLedBlink
jharwinbarrozo
1.1M

Inspect

Cycle Sentry: 24-GHz Radar For Bicyclist Detection

Controls

Properties

Availability & Pricing

Distributor		Qty 1
	Digi-Key	$23.64–$33.15
	LCSC	$25.95–$27.03
	Mouser	$35.61–$37.86

Assets

Footprint

Infineon-BGT24LTR11N16

id=TSNP-16-9

Cyber Sentry.svg

id=Cyber Sentry

HRW.svg

id=HRW_logo

DefaultThumbnail

bitmap.svg

id=WSU_logo

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