eTechnophiles Forum - Recent Topics

DIY an RF power meter Based on STM32F103 + MAX4003

anselbevier — Thu, 26 Mar 2026 09:23:03 +0000

As we all know, Radio frequency (RF) is a very important segment of the IoT industry.

When learning RF technology, power is a critical indicator that must be mastered. Testing RF power usually requires a spectrum analyzer or an RF power meter. However, spectrum analyzers are too expensive for beginners who are new to RF like me, and even the cheapest RF power meters cost hundreds of RMB. For electronics enthusiasts who follow the principle of "spend when you should, save when you can", DIYing an RF power meter is a great alternative.

The first step was to define the functions and design the hardware circuit. To test RF power, a chip called a detector is required. I had not found a suitable option for a long time as it was my first time working with an RF detector, until I saw the power detection module on the E25-C test baseboard, which uses a Maxim MAX4003 for power acquisition.

The MAX4003 RF detector chip supports a frequency range of 100MHz to 2.5GHz, with an input range of -45dBm to 0dBm. It is very cost-effective at only 6 RMB, and its parameters fully meet the requirements. Its stability during testing is also proven in practical use, so I finally chose this detector as the core device of this DIY power meter.

Next was the selection of the MCU chip. I used the well-known STMicroelectronics STM32F103TBU6, which integrates a 12-bit successive approximation ADC (analog-to-digital converter), a 72MHz Cortex-M3 ARM processor, and 128KB of on-chip program memory. The main reasons for choosing it are its QFN36 package and integrated USB controller.

For the display part, a 1.3-inch monochrome LCD screen with ST7565 main controller is used, which communicates via the SPI interface and has a resolution of 128*64. It is fully sufficient for displaying collected data and other information.

In addition, a Texas Instruments OPA333A high-precision operational amplifier is used to amplify the analog signal output by the detector and send it to the ADC pin of the MCU. A GT20L16S1Y chip provides the Chinese character library. The power supply adopts a TYPE-C port, and the voltage is regulated by ME6211 to supply power for the chips. A REF3033AIDBZR reference chip is used to provide the reference source for the ADC.

After the hardware selection and circuit design were completed, the software design was carried out. STM32CUBEMX was used for project configuration, and development was based on HAL library functions. After initializing the ADC, the HAL_ADCEx_Calibration_Start function was used to self-calibrate the ADC. The TIM2 timer was enabled and the interrupt was activated for regular collection of the voltage value output by the RF detector. The ADC performs cyclic collection 10 times and calculates the average value to implement software filtering. For the convenience of wiring during PCB design, the hardware SPI interface of the MCU was not used to operate the screen and the character library chip, so the IO port was used to simulate the software SPI timing to operate the LCD screen and read/write the character library chip.

In addition to the 16*16 GB2312 Chinese character library and character library, the GT20L16S1Y character library chip also has 64KB of freely erasable space from address 0x6FFFF to 0x7FFFF (start address 0X7000), including 16 sectors. This storage space is used to store power calibration parameters.

In addition, necessary functions such as compensation settings have been added. Since the input signal of MAX4003 cannot exceed 0dBm, most signals need to be tested in conjunction with an external attenuator, so software compensation is required for accurate readings. 10 sectors are set to store 10 frequency points, compensation and calibration parameters. To make it easy to set these parameters, a setting menu is written, through which you can select the current frequency point, set the current software compensation and frequency, calibrate the current frequency, save the set parameters and other functions.

During testing, an external high-precision RF signal source was used. It was found that the MAX4003 chip has excellent linearity in the range of -7dBm to -43dBm, so a trade-off was made: 31 calibration data acquisitions were carried out from -10dBm to -40dBm and saved as an array. When the data is measured, the nearest low value is queried from the 31 sets of data for display, and the decimal value between the nearest high value and low value is calculated. After measurement, the test accuracy is excellent, which meets my needs for power measurement as an RF beginner.

The preliminary functional design of the small power meter has been completed. The hardware reserves the TP4055 battery management chip and independently controllable power management. A battery will be added to this small power meter later to use it as a portable power meter.

esp32 diagram connection

wmughal — Wed, 18 Mar 2026 06:39:50 +0000

i never use esp32 before i get diagram from claude i want to u too guys to checi s this diagram ok i have attached with this. u

wiring_v3_470fix.png

Motor driver not working properly

Noochee — Fri, 20 Feb 2026 22:50:49 +0000

I built an obstacle avoiding robotic car using Arduino, dc motors and a motor driver(L293D) , ultrasonic sensor and servo, i added LCD, a buzzer, an LED and a bluetooth module, but it's getting overloaded i guess and it doesn't work, what do i do?

Bluetooth Speaker won't turn on

servitec — Tue, 20 Jan 2026 07:00:52 +0000

I know is not probably the best place for a newbie, the AI somehow helps but I definitely prefer go with the experts. I am fascinated with the laws of electronic, but more than ever I know it demands a serious compromise to enter this amazing world.

Board Description: HXYT-A0-665-REV1.1 (A bluetooth speaker)
The speaker wont turn on, is doing nothing.
SIDE A
Compt.1= 56HS5, B310B (5 pins)
Compt.2= J6 (3 pins) ?
Compt.3 4004A, 33580KM
Side B
Compt.1= 4R7 (inductor)
Compt.2= SS54 (SCHOTTKY BARRIER RECTIFIER)
Compt.3= M8889, Y4D371 (8 Pins) ?
Compt.4 PNSA15E7E, X0B253, 2359

--When connected the battery in the terminals, it shows normal (aprox 5V)
--I tested the negative and positive spots in reverse of battery connector and off course no shorted
--When first tested pin C of power button, it shows 0.840V, after some tests is showing 2.4V when first push the power button it drops to 0V but now no more drops and it gets 2.4 V no matter if push the power button
--Tested all capacitors of Side A and all of them are ok, also the capacitor X which is connected to the Compt.3, the component 3 seems to be a DC-DC converter, the capacitor X is in parallel of pins 4 and 6. When checking the VIN in Compt.3 (pin5) is ok, but when I push the power button there is no VOUT (pin1)
--When connected to the charger, the device’s charging led turns on and the board battery terminals shows the charging voltage.

In Side B

We can see the battery port, the left pin is the + one, that pin goes to the compt.1 through pad named in the image as “pad positive pin”, then the compt.1 is connected to the compt.2 (I tested both and they seem to be ok). I tested all capacitors in Side B, all of them are ok except capacitor X. The capacitor X is connected to the pin that is marked with a yellow face sticker in compt.4, and I'd like to have the PCB's information or at least the compt.4's (or the M8889) in order to know that capacitor values.
What more testing do you recommend me to apply, what is component 2 in side A, what is component 4 in side B, is it a multiplexer? What is component 3 in side B, is it a switch IC? What recommendations can you give me when is hard to find a component by its code?

Side-A.jpg

How can I safely power a BLDC motor from a hard disk drive?

Anil_Tech — Tue, 28 Oct 2025 05:32:49 +0000

I have a brushless DC motor taken from an old hard disk drive and I want to power it safely for testing or small DIY applications. Since these motors are usually designed for specific control circuits, I’m not sure about the correct voltage, current, and driving method.

What’s the safest way to power and control a hard drive BLDC motor?

Should I use a dedicated ESC, a custom driver circuit, or a microcontroller-based solution?
Any tips for determining the correct pinout and avoiding damage to the motor would also be helpful.

How can servo jitter be reduced in Arduino projects?

Anil_Tech — Tue, 21 Oct 2025 06:24:54 +0000

I’m controlling a servo motor using an Arduino, but it occasionally jitters even when it’s supposed to hold a fixed position. The power supply seems stable, and the signal wire is properly connected. What are the common causes of servo jitter in Arduino projects, and what are the best methods to minimize or eliminate it?

Are there any hardware or software techniques—like adding capacitors, using separate power sources, or applying code-based filtering—that can help achieve smoother servo movement?

SPI vs I2C vs UART: which interface should I use for my application and why?

techy ishan — Fri, 10 Oct 2025 05:04:48 +0000

I need to pick one interface before finalizing my PCB and firmware. Short on‑board sensor links; priorities are minimal pins, low power, and reliable data. Which would you choose and why?

DMM in mA mode causes ~0.6 V drop — normal burden voltage? How can I minimize it?

JannikTechy — Thu, 09 Oct 2025 05:21:09 +0000

I’m measuring the current draw of a low-voltage load and noticed my handheld DMM, in mA mode, is dropping about 0.6 V across itself. Is that normal “burden voltage,” and what’s the best way to reduce it?

How do I choose the right op-amp for audio applications?

Roshan — Mon, 29 Sep 2025 05:28:54 +0000

When it comes to audio circuits, I’ve seen many people emphasize the importance of choosing the right op-amp, since it can significantly affect noise, distortion, and overall sound quality.

What factors should be considered when selecting an op-amp specifically for audio applications? For example, how important are parameters like slew rate, input noise, bandwidth, or THD+N (Total Harmonic Distortion + Noise)?

Are there certain op-amp families that are generally preferred for high-quality audio, and how do they compare to using general-purpose op-amps?

How does capacitor ESR affect decoupling performance?

JannikTechy — Tue, 23 Sep 2025 04:42:03 +0000

I often see discussions about choosing the right decoupling capacitor values, but I’ve also read that the ESR (Equivalent Series Resistance) of a capacitor plays an important role in how effective it is.

How exactly does ESR affect the performance of a decoupling capacitor in power supply filtering and noise suppression?

Are there cases where low ESR capacitors are always preferred, or can higher ESR sometimes be beneficial? What are the best practices for considering ESR when selecting capacitors for decoupling in digital or analog circuits?