Checking for Low Voltage Alerts on the Raspberry Pi

 

When starting out with your Raspberry Pi there is a chance that you will run into a low voltage warning. This warning is letting you know that your Raspberry Pi is suffering from under voltage and may not operate as intended.

Simply put, the Pi is not being delivered enough power. This lack of power means the CPU and other components can both under perform and perform erratically.

Typically you will only run into these issues when using a non-official power supply with your Raspberry Pi. This is because the Pi’s have fairly tight power requirements that most USB chargers will not satisfy.

Newer Pi’s such as the Pi 4 has made these requirements even stricter. Just because a power supply worked with an older Pi, doesn’t mean you won’t run into under-voltage errors with a new Raspberry Pi.

There are a few ways that your Raspberry Pi will attempt to warn you about low voltage issues. Both the desktop and terminal versions of Raspberry Pi OS have built-in warnings about under voltage.

Below we will quickly run through various versions of the warning that indicate an issue with low voltage.

Looking for the Under-voltage Warning in Raspberry Pi OS Desktop

Raspberry Pi OS shows you a visual warning when the voltage supplied to the device is low.

Depending on what version of the operating system that you are using, this error may appear differently.

Original Under-Voltage Warning

On older versions of Raspberry Pi OS (Raspbian), the undervoltage issue was indicated by the presence of a yellow thunderbolt in the top-right corner of your screen.

If you see this thunderbolt appear on your screen, you will need to take steps to improve the supply of power to your Pi.

 

New Low Voltage Warning

This low voltage warning has been significantly improved with recent versions of Raspberry Pi OS. It now clearly lets you know what exactly is happening rather than using a graphical symbol.

This low voltage warning will appear in the top-right corner of your desktop and display text indicating that you should check your Raspberry Pi’s power supply.

Checking Terminal for the Low Voltage Warning

There are a couple of ways to check to see whether your Raspberry Pi is running into low voltage issues within the terminal.

Whenever your Raspberry Pi detects under-voltage, it will print a message to the terminal. This message will appear, a bit like what we have below.

You don’t want to wait around for this message to appear, there are couple of methods you can use to check this manually.

Using the vcgenmcd Command

One of the easiest ways to check for low voltage is by utilizing the “vgencmd” command on your Raspberry Pi.

Using this command, we can retrieve various information from the hardware itself. One of these things is the status of the CPU/GPU.

A) Using the following command on your Pi, you can check whether it’s processor has been throttled. 

 

B) If your Raspberry Pi is experiencing throttling due to under-voltage, you will see the following message.

 

This number basically tells that your Raspberry Pi has detected under-voltage and that it is currently throttling the processor. It also tells us that the CPU has previously had an under-voltage event that throttled the processor.

If you want a better understanding of how this value is calculated you can reference our table below.

 

Checking the Kernel Message Buffer

It is also possible to check the kernel message buffer for messages about your Raspberry Pi experiencing low voltage.

Every time the kernel polls the hardware and detects an under-voltage event, it will write a message to this buffer.

A) To check this message buffer, you will need to use the “dmesg” command on your Raspberry Pi.

This command will output the content of the kernel message buffer, which will include any messages

 

B) After using this command, you will get a large amount of text. You can scroll through this text, looking for the following message.

If you see this message, you should look into replacing the power supply for your Raspberry Pi.

C)  Alternatively, you can use the following command to use “grep” to look through the message buffer instead.

 

With this command, we are using a pipe (|) to pass the result of dmesg to the grep tool.

The grep tool will then pass through the text looking for the specified text, which in our case is “under-voltage detected“.

By using the “-i” option, we are telling that it should ignore the case of any letters in the message when making a match.

Additionally, we use the “-C 3” option to print three lines before and after any matches. This option helps find anything else that may have occurred before and after the under-voltage event.

 

How to fix the Low Voltage Warning on the Raspberry Pi

Low voltage warnings are typically caused by an inadequate power supply connected to your Raspberry Pi. The easiest solution to this is to buy and replace the existing power supply.

Purchase an Official Power Supply

The best power supplies for the Pi are always going to be the official ones. These are developed by the Raspberry Pi foundation and are tested thoroughly to ensure they easily satisfy the power requirements.

When using a Raspberry Pi, we recommend that you always stick with the official power supplies as they significantly reduce the chances of your running into issues.

Any retailer referenced on the Pi website should provide you a verified official product.

Be careful when using retailers not referenced on the official website, as there have been several attempts to create cheap knock-offs of the official products.

 

Disabling the Low Voltage Warning (not recommended)

It is also possible to disable the low voltage warning on your Raspberry Pi. However, this is not recommended at all. You will likely run into various issues with your device when using an inadequate power supply.

If you want to ignore this error and disable the under-voltage warning, you can follow the steps below.

These steps will focus on your Raspberry Pi, but you can complete these steps with the SD card inserted into your computer.

1) To disable the low voltage warning, we will need to modify the boot config file.

You can begin modifying this file by running the following command on your device.

 

This config file is available on the boot partition when you plug the SD Card on your Raspberry Pi.

2)  Within this file, you will need to add the following line to the bottom of the file. By setting this value to 1, we are telling it to disable all warning overlays.

 

Please note this means you will no longer receive any more warnings about your Pi not receiving enough voltage.

3) Once you have added this line, save the file by pressing CTRL + X, then Y, followed by the ENTER key. 

4)  We also need to remove the “battery monitor” plugin. This plugin is responsible for showing the notification you may see in the top-right corner of your screen.

You can remove this LXPanel plugin by using the following command on your device.

 

5)  For this change to take effect, you will need to restart your Raspberry Pi.

You can restart by using the following command in the terminal.

 

 

 

 

 

 

 

 

 

 

 

Connecting my IC-9100 to the PC for WSJT-X

I've been wanting to write this down for a long time, but just kept the bits of info on my computer for some reason, so here it is:

Please Note: This is my preference, 

Radio: Icom IC-9100 - maybe IC-7300

 

 

 

 

 

 

 

 

 

 

 

 

Normal PC: Windows 10

Inter-connect:  U5-Link from Aliexpress

This is how I connected the three together:

Also you need to follow the Icom Manual to download the correct USB driver

Pg12: (of the manual)

About the USB driver:
The USB driver and the installation guide can be
downloaded from our website.
➥ http://www.icom.co.jp/world/index.html
The following items are required:
PC
• Microsoft® Windows® XP,
Microsoft® Windows Vista® or
Microsoft® Windows® 7 OS
• A USB 1.1 or 2.0 port
Other items
• USB cable (purchase separately)
• PC software (such as optional RS-BA1 or CS-
9100)
NEVER connect the transceiver to a PC until the
USB driver installation has been completed.
About the modulation input:
Select “USB” in the Set mode item “DATA OFF
MOD” or “DATA MOD.” The modulation input level
from the USB jack can be set in the Set mode item
“USB MOD Level.” (p. 167)

 

I also used the following settings for data mode on the radio:

 

 

I hope that this could help some people get going.

73 de Rodger

 

Which Coax Cable to use for VHF/UHF Satellite Comms

I got a Cushcraft A27010S Yagi

for Christmas from the family which has the UHF elements missing, so while waiting for these from the supplier, I thought I should investigate what coax to use to go to my Icom IC-9100.

I would have to take out the connector shown in the picture and feed two cables to the radio to work split frequency for the satellites.

One can check out Coax reference sheets and they all seem to show similar but different figures.

I was initially thinking the RG-58 c/u would do, but was told that wouldn't cut the mustard and was soon amazed by going through some charts.

I came to three possible solutions, RG-8, RG-213, or LMR-400.

To my amazement the LMR-400 is hand down the best option for loss of signal. Even if I wanted to use it for HF, it looks pretty good.

 

I guess my next step is to find the cheapest price getting the cable and crimping machine and connectors to connect everything together.

Here's a list of AMATEUR RADIO SATELLITES

Leave your comments and suggests for me.

RECEIVING AND DECODING GREENCUBE CUBESAT

About COAX cable:

This study has come about because I wanted to understand what I was doing with my NanoVNA and how different coax cables where affected with different frequencies:

RG and UR coax cable references

Over the years systems developed whereby standard number systems. This enabled coax made by different manufacturers to conform to the same standard.

Over the years two basic systems evolved for defining RF cables. 

1. One originated in the United Kingdom and its type numbers all start with UR. 

2. The other system is American with type numbers commencing with the letters RG.

• UK UR system for coax cable types:   The UR system as defined in the UK and is still widely used for coaxial cable. UR standard for Uniradio, and later the URM series stands for Uniradio Metric.
• USA RG systems for coax cable types:   The RG series was originally used to specify the types of coax cables for military use, and the specification took the form RG (RG from Radio Guide) plus two numbers. In some instances these numbers were followed by the letter U which indicated it was for multiple uses. These types of coax cable were all listed in the MIL-HDBK-216 which is now obsolete. Although full MIL specifications are now officially used for specifying most components for military use, the RG series of RF cables continued to be used because of its widespread acceptance. However it should be noted that the RG specifications are no longer maintained so there is no complete guarantee to the exact specification for the particular type of coax cable

Properties of Popular Coaxial Cables

Note that attenuation values are given at 400 MHz, but can - and do - often have significantly different values at other frequencies. Always check with a coaxial cable vendor for values specific to the type you plan to use.

Type (/U)	MIL-C-17	Z0(Ω)	Dielectric Type	Capacitance (pF/ft)	O.D. (in.)	dB/100 ft @400 MHz	Vmax (rms)	Shield
LMR-100A		50.0	FE	31	0.110	14	2,000	Braid+Foil
LMR-195		50.0	FE	25	0.195	7.0	3,000	Braid+Foil
LMR-200		50.0	FE	24	0.195	6.5	3,000	Braid+Foil
LMR-300		50.0	FE	24	0.300	4.0	5,000	Braid+Foil
LMR-400		50.0	FE	24	0.405	2.5	8,000	Braid+Foil
LMR-500		50.0	FE	24	0.500	2.0	8,000	Braid+Foil
LMR-600		50.0	FE	23	0.590	1.6	8,000	Braid+Foil
LMR-900		50.0	FE	23	0.870	1.1	8,000	Braid+Foil
LMR-1200		50.0	FE	23	1.200	0.8	8,000	Braid+Foil
RG-4		50.0	PE	31	0.226	11.7	1,900	Braid
RG-5		52.5	PE	29	0.332	7.0	3,000	Braid
RG-5A/B		50.0	PE	31	0.328	6.5	3,000	Braid
RG-6	/2-RG6	76.0	PE	20	0.332	7.4	2,700	Braid
RG-6A	/2-RG6	75.0	PE	21	0.332	6.5	2,700	Braid
RG-8		52.0	PE	30	0.405	6.0	4,000	Braid
9914 (RG-8)		50.0	PE	25	0.403	2.6	300	Braid+Foil
RG-8A		52.0	PE	30	0.405	4.5	5,000	Braid
RG-8X		50.0	PE	26	0.242	8.0	2,500	Braid
RG-9		51.0	PE	30	0.420	5.9	4,000	Braid
RG-9A		51.0	PE	30	0.420	6.1	4,000	Braid
RG-9B		50.0	PE	31	0.420	6.1	5,000	Braid
RG-10		52.0	PE	30	0.463	6.0	4,000	Braid
RG-10A		52.0	PE	30	0.463	6.0	5,000	Braid
RG-11	/6-RG11	75.0	PE	21	0.405	5.7	4,000	Braid
RG-11A	/6-RG11	75.0	PE	21	0.405	5.2	5,000	Braid
RG-12	/6-RG12	75.0	PE	21	0.463	5.7	4,000	Braid
RG-12A	/6-RG12	75.0	PE	21	0.463	5.2	5,000	Braid
RG-17A		52.0	PE	30	0.870	2.8	11,000	Braid
RG-22	/15-RG22	95.0	PE	16	0.405	10.5	1,000	Braid
RG-22A/B	/15-RG22	95.0	PE	16	0.420	10.5	1,000	Braid
RG-23/A	/16-RG23	125.0	PE	12	0.650	5.2	3,000	Braid
RG-24/A	/16-RG24	125.0	PE	12	0.708	5.2	3,000	Braid
RG-34	/24-RG34	71.0	PE	22	0.625	5.3	5,200	Braid
RG-34A	/24-RG34	75.0	PE	21	0.630	5.3	6,500	Braid
RG-35	/64-RG35	71.0	PE	22	0.928	2.8	10,000	Braid
RG-35A/B	/64-RG35	75.0	PE	21	0.928	2.8	10,000	Braid
RG-54		58.0	PE	26	0.245		3,000	Braid
RG-55B		53.5	PE	29	0.200	11.7	1,900	Braid
RG-58	/28-RG58	53.5	PE	29	0.195	11.7	1,900	Braid
RG-58A	/28-RG58	52.0	PE	30	0.195	13.2	1,900	Braid
RG-58B		53.5	PE	28	0.195	14.0	1,900	Braid
RG-58C	/28-RG58	50.0	PE	31	0.195	14.0	1,900	Braid
RG-59/A	/29-RG59	73.0	PE	21	0.242	10.5	2,300	Braid
RG-59B	/29-RG59	75.0	PE	21	0.242	9.0	2,300	Braid
RG-62/A/B	/30-RG62	93.0	ASP	14	0.242	8.0	750	Braid
RG-63/A/B	/31-RG63	125.0	ASP	10	0.405	5.5	1,000	Braid
RG-65/A	/34-RG65	950.0	ASP	44	0.405	16 @5MHz	1,000	Braid
RG-71/A/B	/90-RG71	93.0	ASP	14	0.245	8.0	750	Braid
RG-79/A/B	/31-RG79	125.0	ASP	10	0.436	5.5	1,000	Braid
RG-83		35.0	PE	44	0.405	9.0	2,000	Braid
RG-88		48.0		50	0.515	0.7 @1MHz	10,000	Braid
RG-108/A	/45-RG108	78.0	PE	20	0.235	2.8 @10MHz	1,000	Braid
RG-111/A	/15-RG111	95.0	PE	16	0.478	10.5	1,000	Braid
RG-114/A	/47-RG114	185.0	ASP	7	0.405	8.5	1,000	Braid
RG-119	/52-RG119	50.0	ST	30	0.465	3.8	6,000	Braid
RG-120	/52-RG120	50.0	ST	30	0.523	3.8	6,000	Braid
RG-122	/54-RG122	50.0	PE	31	0.160	18.0	1,900	Braid
RG-130	/56-RG130	95.0	PE	17	0.625	8.8	3,000	Braid
RG-131	/56-RG131	95.0	PE	17	0.683	8.8	3,000	Braid
RG-133/A	/100-RG133	95.0	PE	16	0.405	5.7	4,000	Braid
RG-141/A		50.0	ST	29	0.190	9.0	1,900	Braid
RG-142/A/B	/60-RG142	50.0	ST	29	0.195	9.0	1,900	Braid
RG-144	/62-RG144	75.0	ST	20	0.410	4.5	5,000	Braid
RG-164	/64-RG164	75.0	PE	21	0.870	2.8	10,000	Braid
RG-165	/65-RG165	50.0	ST	29	0.410	5.0	5,000	Braid
RG-166	/65-RG166	50.0	ST	29	0.460	5.0	5,000	Braid
RG-174		50.0		31	0.110	14.7		Braid
RG-177	/67-RG177	50.0	PE	31	0.895	2.8	11,000	Braid
RG-178/A/B	/93-RG178	50.0	ST	29	0.072	29.0	1,000	Braid
RG-179	/94-RG179	70.0	ST	21	0.100	21.0	1,200	Braid
RG-179A/B	/94-RG179	75.0	ST	20	0.100	21.0	1,200	Braid
RG-180	/95-RG180	93.0	ST	15	0.140	17.0	1,500	Braid
RG-180A/B	/95-RG180	95.0	ST	15	0.140	17.0	1,500	Braid
RG-210	/97-RG210	93.0	ASP	14	0.242	8.0	750	Braid
RG-211/A	/72-RG211	50.0	ST	29	0.730	2.3	7,000	Braid
RG-212	/73-RG212	50.0	PE	29	0.332	6.5	3,000	Braid
RG-213	/74-RG213	50.0	PE	31	0.405	5.5	5,000	Braid
RG-214	/75-RG214	50.0	PE	31	0.425	5.5	5,000	Dbl Braid
RG-215	/74-RG215	50.0	PE	31	0.463	5.5	5,000	Braid
RG-216	/77-RG216	75.0	PE	21	0.425	5.2	5,000	Braid
RG-217	/78-RG217	50.0	PE	31	0.545	4.3	7,000	Braid
RG-218	/79-RG218	50.0	PE	31	0.870	2.5	11,000	Braid
RG-219	/79-RG219	50.0	PE	31	0.928	2.5	11,000	Braid
RG-223	/84-RG223	50.0	PE	12	0.211	8.8	1,900	Dbl Braid
RG-302	/110-RG302	75.0	ST	20	0.201	8.0	2,300	Braid
RG-303	/111-RG303	50.0	ST	29	0.170	9.0	1,900	Braid
RG-304	/112-RG304	50.0	ST	29	0.280	6.0	3,000	Braid
RG-307/A	/116-RG307	75.0	80	17	0.270	7.5	1,000	Braid
RG-316	/113-RG316	50.0	ST	29	0.102	20.0	1,200	Braid
RG-391	/126-RG391	72.0		23	0.405	15.0	5,000	Braid
RG-392	/126-RG392	72.0		23	0.475	15.0	5,000	Braid
RG-393	/127-RG393	50.0	ST	29	0.390	5.0	5,000	Braid
RG-400	/128-RG400	50.0	ST	29	0.195	9.6	1,900	Braid
RG-401	/129-RG401	50.0	ST	29	0.250	4.6	3,000	Cu. S-R
RG-402	/130-RG402	50.0	ST	29	0.141	7.2	2,500	Cu. S-R
RG-403	/131-RG403	50.0	ST	29	0.116	29.0	2,500	Braid
RG-405	/133-RG405	50.0	ST	29	0.086	13.0	1,500	Cu. S-R

Coax Type	Characteristic impedance	Outside diameter	Velocity factor	Atten @ 100 MHz	Atten @ 1000 MHz	Comments
UR43 / URM43	50	5	0.66	1.3	4.46	Plain copper wire braid
UR57 / URM57	75	10.3	0.66	0.63	2.3	Similar to RG11A/U – plain copper wire braid.
UR67 / URM67	50	10.3	0.66	0.66	2.52	Similar to RG213/U – plain copper wire braid
UR74 / URM74	50	22.1	0.66	0.33	1.4	Plain copper wire braid
UR76 / URM76	51	5	0.66	1.7	7.3	Similar to RG58C/U, plain copper wire braid
UR77	75	22.1	0.66	0.33	1.4
UR79	50	21.7	0.96	0.17	0.6
UR90	75	6.1	0.66	1.2	4.1	Similar to RG59B/U
URM91	50	11.0	0.66			Double plain copper wire braid

• RG stands for Radio Guide.
• U stands for Universal

Properties of Coaxial Cable Dielectrics(c = speed of light in a vacuum)
Dielectric Type	Time Delay(ns/ft)	Propagation Velocity
Solid Polyethylene (PE)	1.54	0.659c
Foam Polyethylene (FE)	1.27	0.800c
Foam Polystyrene (FS)	1.12	0.910c
Air Space Polyethylene (ASP)	1.15-1.21	0.840c-0.880c
Solid Teflon (ST)	1.46	0.694c
Air Space Teflon (AST)	1.13-1.20	0.850c-0.900c

 

 

Capacitor Dielectrics & Descriptions

Here are few of the most commonly used dielectric materials for capacitors. A brief description and application examples are provide for many.

• Air-Gap:
  • Low dielectric loss and offers good cooling. Large-valued tunable capacitors (like in old radios) are often made this way.
• Aluminum:
  • Very high capacitance density (capacitance to volume). High dielectric leakage - prone to exploding.
• Ceramic:
  • Ceramic dielectric types are differentiated by the temperature coefficient of capacitance, and the dielectric loss. Available in 1% tolerance for values up to about 1 µF, typically made from Lead zirconate titanate (PZT) ferroelectric ceramic. Capacitance can change with applied voltage (piezoelectric effect)
    • C0G or NP0 (negative-positive-zero, ±0): Typically 4.7 pF to 0.047 µF, 5%. High tolerance and temperature performance (flat over temp). Larger and more expensive. Lowest losses, used in filters, as timing elements, and for balancing crystal oscillators.
    • X7R: Typical 3300 pF to 0.33 µF, 10%. Good for non-critical coupling, timing applications. Subject to microphonics.
    • Z5U or 2E6: Typical 0.01 µF to 2.2 µF, 20%. Good for bypass, coupling applications. Low price and small size. Subject to microphonics.
• Combination Film:
  • Combination polyester (Mylar) and polypropylene. Extremely low temperature coefficient in the 0° C to 85° C temperature range. Volumetric efficiency similar to polycarbonate.
• Glass:
  •  Extremely stable & reliable
• Kapton Film:
  • Electrical properties similar to Mylar with a much higher operating temperature going up to 250° C. A higher cost than Mylar.
• KF (Polymer) Film:
  • Extremely high volumetric efficiency with about 4x the "K Factor" of Mylar, making it about 1/4 the size. Higher DF and lower IR are its disadvantages along with cost.
• Mica:
  • Chemically inert nature means it does not change physically or chemically with age and it has good temperature stability. Plain mica can absorb moisture, but metallized mica and silver mica are more resistant to moisture.
• Paper Film:
  • Paper or Kraft Paper is the oldest of the film capacitor dielectrics. The paper must be impregnated with Epoxy, Wax, Oil, or other suitable impregnate. It is still popular for high voltage and AC rated capacitors operating at lower frequencies. Paper is also wound with plastic dielectrics in combination dielectric capacitors. Its hydroscopic nature allows moisture to degrade performance over time.
• Polyamide (plastic film):
  • Operating temperatures of up to 200ºC. High insulation resistance, good stability and a low dissipation factor. High cost and large size.
• Polycarbonate Film:
  • Lower DF, higher IR, better temperature coefficient and better stability than Mylar with a slightly lower volumetric efficiency. 2nd most popular dielectric.  Polycarbonate capacitors have a 100% voltage rating from -55° C to +125° C.
• Polyester (Mylar) Film:
  • A good general purpose plastic dielectric with relativity low cost and high volumetric efficiency. The most popular of the capacitor dielectrics.
• Polypropylene Film:
  • Very good temperature coefficient high IR, and low DF make it suitable for AC operation. Usable to 105° C without derating. Popular for AC applications.
• Polystyrene Film:
  • Very good electrical properties and excellent stability are its advantages. The big disadvantage is its operation is limited to below 85° C, and their large size.
• Polysulfone Film:
  • Electrical properties similar to polycarbonate with a very good temperature coefficient and higher operating temperature. Very limited availability in the last few years has limited its use.
• Tantalum:
  • Large capacitance to volume ratio, smaller size, good stability, wide operating temperature range, long reliable operating life. Widely used in miniaturized equipment and computers. Available in both polarized and unpolarized versions, so suitable for AC and DC. Solid tantalums have much better characteristics than wet slug (not permitted in any Mil-Spec equipment) versions.
• Teflon Film:
  • The best electrical properties of all the dielectrics. Extremely high IR, low DF and operation to 250° C. Expensive and physically large.