Go to advanced search

by davidcoton
Sun May 20, 2018 7:56 pm
Forum: General discussion
Topic: Upgrade confusion?
Replies: 20
Views: 674

Re: Upgrade confusion?

... required manual booting from binary toggle switches before it could read the punch tape .... (about 10mins. of the 30 mins. "allocated slot" IIRC :( )) I had to do that once. Just as I finished, someone pointed out that the memory was magnetic cores and therefore non-volatile -- the code was th...
by davidcoton
Sun May 20, 2018 8:15 am
Forum: Troubleshooting
Topic: Can't Get LED to light
Replies: 14
Views: 286

Re: Can't Get LED to light

LTolledo wrote:
Sun May 20, 2018 2:14 am

6. the resistor color band is orange-white-brown-gold (390ohms 20% tolerance)
[pedant]
A gold band represents 5% tolerance. 20% has no band.
[/pedant]
by davidcoton
Thu May 17, 2018 9:56 am
Forum: General discussion
Topic: Effective way to communicate Raspberry Pi with STM32
Replies: 13
Views: 384

Re: Effective way to communicate Raspberry Pi with STM32

Thanks for your suggestions. I will finally consider RS232 for my application. I know that other protocols offer better characteristics, but RS232 would work here. Another question, as I will use MAX3232, should I supply it with 3.3V right? As STM32 and Pi works with 3.3V, I need the charge pump fo...
by davidcoton
Mon May 14, 2018 10:32 pm
Forum: Troubleshooting
Topic: Pin 1 and Pin 2 short circuited
Replies: 9
Views: 293

Re: Pin 1 and Pin 2 short circuited

3V3 to 5V0. The polyfuse won't help in that scenario. Almost certainly time to buy a new Pi.
by davidcoton
Sun May 13, 2018 9:50 pm
Forum: General discussion
Topic: Using your Pi with an SSD (Solid State Drive)
Replies: 22
Views: 1876

Re: Using your Pi with an SSD (Solid State Drive)

jmmec wrote: The Pi boots with (and without) "program_usb_boot_timeout=1"
If you have booted once with that parameter, the OTP bit is set and the longer timeout is permanent. You can only test booting with the shorter timeout on a Pi that has NEVER been booted with program_usb_boot_timeout=1.
by davidcoton
Sun May 13, 2018 9:36 pm
Forum: General discussion
Topic: connecting up to a breadboard
Replies: 7
Views: 166

Re: connecting up to a breadboard

The connector is labelled "P1", right next to that label (visible in your photo) is a rather subtle mark for pin 1.
Also, on the other side of the board, pin 1 has a square pad on the board, while all the other pins have round pads.
by davidcoton
Sun May 13, 2018 9:23 pm
Forum: General discussion
Topic: connecting up to a breadboard
Replies: 7
Views: 166

Re: connecting up to a breadboard

Yes. The pins on your Pi are identical to pins 1-26 on later Pis. You just don't have pins 27-40 -- at least not on the same connector.
by davidcoton
Sat May 12, 2018 8:30 pm
Forum: Advanced users
Topic: raspberry pi b+ to raspberry pi 3
Replies: 12
Views: 402

Re: raspberry pi b+ to raspberry pi 3

Hi all, Well its about mine PI. I have de PI3 model B and NL3PRC he haves an older model I think then I have.I have tried to load the kenrel serveral times but it keeps hanging at boot up with the messages "Critcal error couldnt load the kernel or mount the kernel" Now as I think it looks to me tha...
by davidcoton
Fri May 11, 2018 9:41 pm
Forum: Beginners
Topic: New RPI 3+ won't boot on touchscreen
Replies: 2
Views: 65

Re: New RPI 3+ won't boot on touchscreen

What does the red PoWeR LED do? If it flashes a patttern (4 short 4 long I think) then this indicates an OS that is not updated for Pi3B+. What OS are you using? With or without NOOBS? For plain Raspbian Stretch without NOOBS, put the card back in your Pi3B, do sude apt update sudo apt full-upgrade ...
by davidcoton
Fri May 11, 2018 9:26 pm
Forum: General discussion
Topic: my pi running hot and no i2c
Replies: 9
Views: 436

Re: my pi running hot and no i2c

Been a very busy week so couldn't get back to reply sooner. My uncertainty was about if it helped explain the GPIO destruction not whether it is a high-pass RC circuit. A low pass RC filter circuit has the capacitor in parallel with the load, the resistor in series with the load and it passes only ...
by davidcoton
Fri May 11, 2018 8:37 pm
Forum: Troubleshooting
Topic: Pi 3 crashing at the same time each day
Replies: 14
Views: 490

Re: Pi 3 crashing at the same time each day

So you're saying that the system is rebooting itself and then locking up again and unable to reboot? When I come in the morning it's basically dead, the display is black so there is a signal, the mouse, keyboard have power, and the ethernet jack LEDs are both on as is the power led. The next entrie...
by davidcoton
Thu May 10, 2018 3:32 pm
Forum: Beginners
Topic: Date Time format
Replies: 5
Views: 139

Re: Date Time format

See "datetime.isoformat(sep='T', timespec='auto')" in https://docs.python.org/3/library/datetime.html [pedant] It's an ISO format, not a UTC format. UTC is time regardless of format, the format is specified in ISO 8601. IIRC the displayed time is actually local, not UTC, until the offset is taken in...
by davidcoton
Wed May 09, 2018 8:23 am
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

I did as suggested and reread this entire thread multiple times, following more logic. drgeoff, you are correct, when I remove r2 entirely (no jumper or infinite resistance as you said), Vout (v1) is 2.070157v and Vin (v2) 3.295735 resulting in 26891.27089 ohms. I am assuming this is the 10,000 r1 ...
by davidcoton
Tue May 08, 2018 9:34 pm
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

Sorry I don't have time to write anything in enough detail to be helpful. At present I am not sure where and why your understanding is going awry -- which is why I suggested you need some face to face help. I don't think a "differetial mode" ADC will help (it would mean you could get the voltage acr...
by davidcoton
Tue May 08, 2018 8:31 am
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

According to https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-resistor-circuits/a/ee-voltage-divider I should be using this formula to find r2: r2 = (-v1*r1)/(v1-v2) I haven't checked the source (no time, have to go to work) but that equation gives a negative ...
by davidcoton
Mon May 07, 2018 11:28 pm
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

[...] True, but accuracy and stability are closely related. I think not. High accuracy requires high stability but high stability is not sufficient for high accuracy. For example, a voltage source that is always within 10 ppm of 1 volt might be considered highly stable but if it is supposed to be w...
by davidcoton
Mon May 07, 2018 5:00 pm
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

Only the very short term stability of the reference is important, ie over the time between reading V1 and V2. The measurement method is that of ratio between a known resistance and an unknown one. The real accuracy of the ADC's voltage reference does not matter as long as it is the same when measur...
by davidcoton
Mon May 07, 2018 12:52 pm
Forum: General discussion
Topic: What constitutes "Advanced"
Replies: 18
Views: 661

Re: What constitutes "Advanced"

Being pedantic, the topic is "Advanced users" not "Advanced uses". Subtle but significant difference. :) That adds weight to @joan's theory that it means "Users advanced in years". :lol: Perhaps it is related to the common perception that any computing "thing" that first happened in the second half...
by davidcoton
Mon May 07, 2018 12:46 pm
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

V1 does not need correction because the source impedance of the 3V3 supply is low. I think my conclusion is that V2 does not need correction, but in calculating R2 the input resistance of the the V2 channel (call it Rk) must be taken into account. Agreed. Neither voltage needs correction. But the i...
by davidcoton
Mon May 07, 2018 12:35 pm
Forum: General discussion
Topic: Power supply for raspberry pi 3
Replies: 11
Views: 359

Re: Power supply for raspberry pi 3

I know that this forum is english, but anyone can tell me if this https://produto.mercadolivre.com.br/MLB-995286151-fonte-raspberry-pi-3-inova-v8-original-31a-usb-_JM is a good power supply for Raspberry Pi 3 ? It seems to have the same issues as the Xiaomi charger. You need a supply capable of bet...
by davidcoton
Mon May 07, 2018 12:21 pm
Forum: General discussion
Topic: Power supply for raspberry pi 3
Replies: 11
Views: 359

Re: Power supply for raspberry pi 3

I know that this forum is english, but anyone can tell me if this https://produto.mercadolivre.com.br/MLB-995286151-fonte-raspberry-pi-3-inova-v8-original-31a-usb-_JM is a good power supply for Raspberry Pi 3 ? It seems to have the same issues as the Xiaomi charger. You need a supply capable of bet...
by davidcoton
Mon May 07, 2018 12:15 pm
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

I'm getting myself thoroughly confused in trying to work out which measurements need correction and which don't. :( So please don't accept what follows without some careful checking. V1 does not need correction because the source impedance of the 3V3 supply is low. I think my conclusion is that V2 d...
by davidcoton
Sun May 06, 2018 8:18 am
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

That looks better. Now try the resistance calculation. V 2 =IR 2 (V 1 -V 2 )=IR 1 So: R 2 =V 2 *R 1 /(V 1 -V 2 ) Be careful about the order of calculation! This will work with values in volts(V), milliAmps(mA), and kilOhms (kΩ). The conductance is the inverse of resistance. Conductivity (σ) will req...
by davidcoton
Sat May 05, 2018 11:04 pm
Forum: Troubleshooting
Topic: Trouble in installing Noobs in RS component Release Raspberry Pi3 B+
Replies: 4
Views: 116

Re: Trouble in installing Noobs in RS component Release Raspberry Pi3 B+

Is there a lightening symbol on screen? What are the red PoWeR and gren ACTivity LEDs doing? Lightening symbol and no (or erratic) red LED is a power supply problem. Lightening symbol and red LED flashing (IIRC four long, four short) is an out-of-date software download. In this case straight Raspbia...
by davidcoton
Sat May 05, 2018 10:56 pm
Forum: Beginners
Topic: Electrical Resistance Calculation Help
Replies: 61
Views: 1673

Re: Electrical Resistance Calculation Help

Remove the connection to ch3. Connect the south end of R2 (probe) to 0V. then repeat your mesurements. Removing one connection to the ADC should not affect the reading of the other, unless the ADC design (or your wiring) is deficient. You will need to gather new data for your water samples, and re-c...

Go to advanced search