The base excitation frequency (for hydrogen) is:
63.87 MHz for 1.5 Tesla MRI scanners127.74 MHz for 3 Tesla MRI scannersNote that the excitation frequency is not exactly one frequency but varies spatially based on the gradient field strength.
You can calculate the excitation frequency using
Excitation frequency [MHz] = 42.58 MHz/T * [magnetic field strength in Tesla]
For more info, see mriquestions.com
Only two pins on the ESP32-S2 are capable of being DAC outputs:
GPIO23 is DAC_1GPIO24 is DAC_2Source: ESP32-S2 datasheet
You can use the LEDC timer (typically used for PWM) to output a 50% duty cycle clock with 3.3V P-P amplitude on any output-capable GPIO pin.
First,
#include <driver/ledc.h>
then setup the timer. You only need to do this once on startup, no code in your loop function is required.
/**
* Setup 2.048MHz clock output on GPIO33
*/
ledc_timer_config_t ledc_timer = {
.speed_mode = LEDC_HIGH_SPEED_MODE,
.bit_num = LEDC_TIMER_2_BIT,
.timer_num = LEDC_TIMER_0,
.freq_hz = 2048000
};
ledc_channel_config_t ledc_channel = {
.gpio_num = GPIO_NUM_33,
.speed_mode = LEDC_HIGH_SPEED_MODE,
.channel = LEDC_CHANNEL_0,
.timer_sel = LEDC_TIMER_0,
.duty = 2
};
ledc_timer_config(&ledc_timer);
ledc_channel_config(&ledc_channel);
The ESP32 DAC has a built-in cosine waveform generator. Even though it’s an 8-bit DAC, the waveform looks pretty clean.
For an example on how to generate this wavefrm in firmware, see How to use the ESP32 DAC sine/cosine waveform generator using Arduino / PlatformIO
The ESP32 and its derivatives such as the ESP32-S2 have a built-in sine/cosine waveform generator for the built-in 8-bit DAC.
Using it requires ESP-IDF v5.1+ (see the official example). Using it with Arduino is slightly harder, since the stable version of the arduino-esp32 framework at the time of writing this post is based on ESP-IDF v4.4 which does not provide the DAC cosine generator API.
Therefore, we have to explicitly specify the arduino-espressif32 version (git commit) in platformio.ini:
[env:esp32dev] platform = espressif32 # Commit f9cddfde697b659b9e818ec514f1505d2bd4a8ae is branch esp-idf-v5.1-libs @2022-02-01 platform_packages = framework-arduinoespressif32 @ https://github.com/espressif/arduino-esp32.git#f9cddfde697b659b9e818ec514f1505d2bd4a8ae board = esp32dev framework = arduino
The example main source code is pretty simple:
#include <Arduino.h>
#include <driver/dac_cosine.h>
void setup() {
dac_cosine_handle_t chan0_handle;
dac_cosine_config_t cos0_cfg = {
.chan_id = DAC_CHAN_1, // GPIO26
.freq_hz = 1000,
.clk_src = DAC_COSINE_CLK_SRC_DEFAULT,
.atten = DAC_COSINE_ATTEN_DEFAULT,
.phase = DAC_COSINE_PHASE_0,
.offset = 0,
//.flags.force_set_freq = false,
};
ESP_ERROR_CHECK(dac_cosine_new_channel(&cos0_cfg, &chan0_handle));
ESP_ERROR_CHECK(dac_cosine_start(chan0_handle));
}
void loop() {
// put your main code here, to run repeatedly:
delay(1000);
}If you want to see how the generated waveform looks on an oscilloscope, see How does the ESP32 DAC cosine generator waveform look on an Oscilloscope?
On the MAX11200EEE+ and the MAX112100EEE+, bit 3 of the command byte is named IMPD but this bit is never described in detail in the datasheet.
The meaning of this bit is Immediate power-down. When you set it to 1, the IC will switch to power-down mode. This is evidenced by the power-down example in Table 8 in the datasheet.
The MAX11200EEE+ and the MAX112100EEE+ operate using SPI Mode 0. Therefore, CPHA=0 & CPOL=0.
For more information, see the datasheet.
Based on our Minimal PlatformIO ESP8266 ArduinoOTA example, this is a minimal starting point for your ESP32 program running ArduinoOTA.
#include <Arduino.h>
#include <WiFi.h>
#include <ArduinoOTA.h>
void setup() {
Serial.begin(115200);
/**
* Connect to Wifi
*/
WiFi.begin("MyWifi", "abc123abc");
uint32_t notConnectedCounter = 0;
while (WiFi.status() != WL_CONNECTED) {
delay(100);
Serial.println("Wifi connecting...");
notConnectedCounter++;
if(notConnectedCounter > 150) { // Reset board if not connected after 15s
Serial.println("Resetting due to Wifi not connecting...");
ESP.restart();
}
}
Serial.print("Wifi connected, IP address: ");
Serial.println(WiFi.localIP());
/**
* Enable OTA update
*/
ArduinoOTA.begin();
}
void loop() {
// Check for over the air update request and (if present) flash it
ArduinoOTA.handle();
}
You can leave your platformio.ini at default values, the only aspect you need to change is to set monitor_speed = 115200
[env:esp32dev] board = esp32dev platform = espressif32 framework = arduino monitor_speed = 115200
If you have an URL like
https://logodix.com/logo/1667872.jpg?param=value
and you want to find just the filename extension (.jpg for this example), use the following code:
from urllib.parse import urlsplit import os.path url = "https://logodix.com/logo/1667872.jpg?param=value" path = urlsplit(url).path extension = os.path.splitext(path)[-1] # e.g. ".jpg"
When trying to urlsplit an URL in Python 3:
from urllib.parse import urlparse path = urlparse.urlsplit(remote_image_url).path
you see the following error message:
AttributeError Traceback (most recent call last)
Input In [30], in <cell line: 3>()
1 from urllib.parse import urlparse
----> 3 path = urlparse.urlsplit(remote_image_url).path
4 filename = posixpath.basename(path)
AttributeError: 'function' object has no attribute 'urlsplit'The equivalent of urlparse.urlsplit() in Python 3 is urllib.parse.urlsplit().
Therefore, a working code example is
from urllib.parse import urlsplit path = urlsplit(remote_image_url).path
While trying to import urlparse in Python 3 using
import urlparse
you see the following error message:
--------------------------------------------------------------------------- ModuleNotFoundError Traceback (most recent call last) Input In [29], in <cell line: 1>() ----> 1 import urlparse ModuleNotFoundError: No module named 'urlparse'
In Python 3, urlparse has been renamed to urllib.urlparse. In order to import it, use this line instead:
from urllib.parse import urlparse
While trying to create an InvenTree object using a remote_image URL, you see an error message like
requests.exceptions.HTTPError: {'detail': 'Error occurred during API request', 'url': 'https://inventree-test.mydomain.com/api/company/', 'method': 'POST', 'status_code': 400, 'body': '{"remote_image":["Downloading images from remote URL is not enabled"]}', 'headers': {'AUTHORIZATION': 'Token 6daae3817756e9c1a3603b14d9582e61f50db388'}, 'params': {'format': 'json'}, 'data': {'name': 'DigiKey', 'website': 'https://www.digikey.de/', 'remote_image': 'https://logodix.com/logo/1667872.jpg', 'description': '', 'is_manufacturer': False, 'is_supplier': True, 'is_customer': False, 'currency': 'EUR'}}
Open the InvenTree webinterface, open Server Configuration on the left
and enable Download from URL.
The setting will be effective immediately. There is no need to click any Apply button or restart the server.
This post is based on How to install InvenTree using docker in just 5 minutes and uses the auto-generated docker-compose.yml from there. However it should be useable for almost any setup.
The setup is pretty standard since the inventree proxy container runs the webserver on port 80. Therefore, you don’t even have to explicitly specify a load balancer port
In your docker-compose.yml, add the following labels to the inventree-proxy container:
For more details on the base Traefik setup, see Simple Traefik docker-compose setup with Lets Encrypt Cloudflare DNS-01 & TLS-ALPN-01 & HTTP-01 challenges
labels:
- "traefik.enable=true"
- "traefik.http.routers.inventree-mydomain.rule=Host(`inventree.mydomain.com`)"
- "traefik.http.routers.inventree-mydomain.entrypoints=websecure"
- "traefik.http.routers.inventree-mydomain.tls.certresolver=cloudflare"
- "traefik.http.routers.inventree-mydomain.tls.domains[0].main=mydomain.com"
- "traefik.http.routers.inventree-mydomain.tls.domains[0].sans=*.mydomain.com"
The following script is an automated installation script for InvenTree that fetches the current docker-compose.yml and other configs from GitHub, modifies them so that only local directories are used for storage and then setups InvenTree.
First, create a directory such as /opt/inventree-mydomain. I recommend to choose a unique directory name and not just inventree to keep instae
#!/bin/sh wget -O nginx.prod.conf https://github.com/inventree/InvenTree/raw/master/docker/production/nginx.prod.conf wget -O docker-compose.yml https://github.com/inventree/InvenTree/raw/master/docker/production/docker-compose.yml wget -O .env https://github.com/inventree/InvenTree/raw/master/docker/production/.env sed -i -e 's/#INVENTREE_DB_USER=pguser/INVENTREE_DB_USER=inventree/g' .env sed -i -e "s/#INVENTREE_DB_PASSWORD=pgpassword/INVENTREE_DB_PASSWORD=$(pwgen 30 1)/g" .env sed -i -e "s/INVENTREE_WEB_PORT=1337/INVENTREE_WEB_PORT=$(shuf -i 1024-65535 -n 1)/g" .env sed -i -e "s/#INVENTREE_ADMIN_USER=/INVENTREE_ADMIN_USER=admin/g" .env sed -i -e "s/#INVENTREE_ADMIN_PASSWORD=/INVENTREE_ADMIN_PASSWORD=$(pwgen 30 1)/g" .env sed -i -e "s/#INVENTREE_ADMIN_EMAIL=/[email protected]/g" .env sed -i -e 's/COMPOSE_PROJECT_NAME=inventree-production//g' .env # Enable cache sed -i -e "s/#INVENTREE_CACHE_HOST=inventree-cache/INVENTREE_CACHE_HOST=inventree-cache/g" .env sed -i -e "s/#INVENTREE_CACHE_PORT=6379/INVENTREE_CACHE_PORT=6379/g" .env # Use direct directory mapping to avoid mounting issues sed -i -e "s%- inventree_data:%- $(pwd)/inventree_data:%g" docker-compose.yml # ... now we can remove the volume declarations from docker-compose.yml sed -i -e '/^volumes:/,$d' docker-compose.yml sed -z -i -e 's#profiles:\s*- redis\s*##g' docker-compose.yml # Make redis start always, even without docker-compose --profile redis # Use standard docker-compose directory naming to facilitate multiple parallel installations sed -z -i -e 's#container_name:\s*[a-zA-Z0-9_-]*\s*##g' docker-compose.yml # Remove container_name: ... statements # Create data directory which is bound to the docker volume mkdir -p inventree_data # Initialize database docker-compose up -d inventree-cache inventree-db # database initialization needs cache docker-compose run inventree-server invoke update
After that, you can check .env for the randomly generated INVENTREE_ADMIN_PASSWORD and INVENTREE_WEB_PORT.
Now you can enable autostart & start the service using systemd, for more details see our post Create a systemd service for your docker-compose project in 10 seconds:
curl -fsSL https://techoverflow.net/scripts/create-docker-compose-service.sh | sudo bash /dev/stdin
Don’t forget to configure your reverse proxy to point to InvenTree.
While trying to create a Company using the InvenTree API you see an error message like
requests.exceptions.HTTPError: {'detail': 'Error occurred during API request', 'url': 'https://inventree.techoverflow.net/api/company/', 'method': 'POST', 'status_code': 400, 'body': '{"remote_image":["Server responded with invalid status code: 403"]}', 'headers': {'AUTHORIZATION': 'Token 340fdf063d5433b83bc37c50a4b52ee2f246021b'}, 'params': {'format': 'json'}, 'data': {'name': 'DigiKey', 'website': 'https://www.digikey.de/', 'remote_image': 'https://www.digikey.de/-/media/Images/Header/logo_dk.png', 'description': 'Test', 'is_manufacturer': False, 'is_supplier': True, 'is_customer': False, 'currency': 'EUR'}}
The core issue here is:
{"remote_image":["Server responded with invalid status code: 403"]}InvenTree tries to download the remote_image URL – but that URL can’t be downloaded and the upstream server (digikey.de in this case) generates a 403 response. This is often the case when an URL can only be downloaded with correct Referer headers or other headers set to a specific value.
In order to fix this issue, change the remote_image URL to an image URL which can be fetched correctly.
Sometimes this issue can also arise if the IP address of the InvenTree server is blocked by the server serving the image. This can easily found out by trying to download the given image URL from the server running inventree using wget [URL].
The equivalent of Arduino’s millis() function when using the STM32 HAL is
HAL_GetTick()
The ticks occur once every millisecond, so this will also give you a millisecond timer that will overflow after some time equivalently to how millis() overflows.
While trying to adb pair to your device, you see an error message like
$ adb pair 10.9.1.104:34879 Enter pairing code: 232521 error: unknown host service
and the pairing fails
You are not running the (correct version?) of the ADB server.
Run
adb kill-server
and then retry your adb pair command.
If that doesn’t work, reboot your device.
In case you see the following error for your Angular application in your JS console:
main.ts:6 ERROR NullInjectorError: R3InjectorError(AppModule)[MyService -> HttpClient -> HttpClient -> HttpClient]:
NullInjectorError: No provider for HttpClient!
at NullInjector.get (core.mjs:7599:27)
at R3Injector.get (core.mjs:8020:33)
at R3Injector.get (core.mjs:8020:33)
at R3Injector.get (core.mjs:8020:33)
at injectInjectorOnly (core.mjs:634:33)
at Module.ɵɵinject (core.mjs:638:60)
at Object.MyService_Factory [as factory] (my.service.ts:8:38)
at R3Injector.hydrate (core.mjs:8121:35)
at R3Injector.get (core.mjs:8009:33)
at ChainedInjector.get (core.mjs:12179:36)you need to add HttpClientModule to your app.module.ts.
First, import HttpClientModule at the top of app.module.ts:
import { HttpClientModule } from '@angular/common/http';
After that, add
HttpClientModule,
to the imports: [...] section of your @NgModule, for example:
@NgModule({
declarations: [
AppComponent,
],
imports: [
HttpClientModule,
BrowserModule,
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule { }
After that, your error should have disappeared
Using Angular’sHttpClient in a service to fetch a JSON is pretty straightforward. In this example, we’ll fetch a JSON array.
Note that it’s recommended to create your own TypeScript interface for improved static typing, but nevertheless starting with any[] is often a good idea since it allows you to get started quickly.
public loadMyJSONArray(): Observable<any[]> {
return this.http.get<any[]>(`/api/my-api`);
}import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';
@Injectable({
providedIn: 'root'
})
export class MyService {
constructor(private http: HttpClient) {
}
public loadMyJSONArray(): Observable<any[]> {
return this.http.get<any[]>(`/api/my-api`);
}
}
Assuming you have a Python script server.py that you want to auto-reload every time the file changes, use the following script using nodemon:
nodemon -w . --exec python server.py
The -w . tells nodemon files to watch for changes of all files in the current directory (.)
I generally recommend creating a script start.sh to automatically run this command:
#!/bin/sh nodemon -w . --exec python server.py
and then make it executable using
chmod a+x start.sh
Now you can run it using
./start.sh