BBS:      TELESC.NET.BR
Assunto:  Re: PI PICO W minimum voltage..
De:       The Natural Philosopher
Data:     Wed, 13 May 2026 14:06:07 +0100
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On 13/05/2026 12:12, druck wrote:
> On 12/05/2026 14:04, The Natural Philosopher wrote:
>> On 11/05/2026 23:38, Computer Nerd Kev wrote:
>>> The Natural Philosopher  wrote:
>>>>
>>>> This is a bit of a puzzle. My oil sensor stopped transmitting last
>>>> night. I replaced the batteries just now and its working again. The
>>>> voltage from is 3 x AA supply had dropped to 4.2V. This is supposed to
>>>> be enough to work a PICO W off? And IIRC on test it worked down to
>>>> around 3.8V or so.
>>>>
>>>>
>>>> Anyone know more?
>>>
>>> I don't know the Pico's power specs, but maybe there's resistance
>>> on one of the electrical connections, such that the voltage drops
>>> more under load than where and when you measured it?
>>>
>> I measure at the far end of the chain
> 
> How? Multimeter, USB power measuring dongle, oscilloscope.
> 
Sigh

The Pi PICO W has three ADCs on board and one is  connected directly to 
VSYS by a voltage divider. I transmit that data every time the device 
successfully activates.

This is the relevant code frangment
     while (TRUE)
		{
		temperature = read_temperature();
		printf("getting distance\n");
        		distance=get_distance();
         	voltage=get_battery_voltage();
  // check wifi is up and connect/reconnect as necessary..if cant 
connect in 10 goes, give up.
		for(i=0;i<10 ;i++)
			{
			printf("Attempting to connect to wifi %s\n",ssid);
			cyw43_arch_wifi_connect_timeout_ms(ssid, password, 		 
CYW43_AUTH_WPA2_AES_PSK, 20000);
			sleep_ms(1000); // allow DHCP handshake to take place
			if ((cyw43_tcpip_link_status(&cyw43_state,CYW43_ITF_STA)) == 
CYW43_LINK_UP)
				break;
			}
		if(i==10)
			{
			suicide();
			sleep_ms(1000);
			}

and so on.

The battery voltage is read after wifi initialisation but before a 
connection is established.
The log file on the wifi hotpoint reveals no successful connections at 
all in the last 30 hours

Not even one that aborts later from low/bad signal.


This is the last transmission

OIL-SENSOR
OIL-TANK
-79dBm
78.47cm
5.9C
4.5V
11/05/2026 21:52:47


> The first two will average the voltage readings over a short period. You 
> really need a scope to spot transient drops, such as when the Pico is 
> transmitting over WiFi.
> 

Pico should never gulp more than 200mA and that is well within a dry 
cell . There is a 220uF cap as well to handle spikes.

 From raspberry Pi forum

"Re: Pico W power consumption

"Sun Aug 07, 2022 1:32 pm
Using a battery pack with 3 AA batteries, reading 4.6V, I measured 52 mA 
using wifi and the LED. While starting up it did spike up to ~150 mA 
briefly. "


Anyway it's all irrelevant as the new batteries stopped working almost 
immediately, Last reading was 4.5V

I suspect it us the Triffid like growth of the Russian vine over the oil 
tank plus a stiff breeze making the leaves flutter.

I will remove the batteries and check them with a multimeter. I reloaded 
with the cheapest possible  amazon 'value' cells and it is entirely 
possible that they are in fact utter shit

I will actually order energizer lithium AAs from Amazon and try those. 
They have a far higher OCV (up to 1.75v) and netter sustained discharge 
voltages as well

When I tested the unit indoors for a month with an admittedly better 
wifi connection it operated down to under 4V measured by the ADC. 
Limiting factor was the ultrasonic sensor. Not the wifi.

Ah well, These things are sent to try us.

Let me see what is going on with the unit now...

-- 
?Puritanism: The haunting fear that someone, somewhere, may be happy.?

H.L. Mencken, A Mencken Chrestomathy


--- PyGate Linux v1.5.14
 * Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

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