Go to advanced search

by PiGraham
Fri Aug 03, 2018 7:08 am
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

If you need more light use lower value resistors from 3.3V There is no call (but no harm) for using additional transistors to switch these small LEDs. The GPIO can easilly supply ten times the current you estimate to be " in the neighbourhood of 1mA" I agree, if he has the skills and tools to solde...
by PiGraham
Thu Aug 02, 2018 9:47 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

If you need (much) more light you will need a transistor to switch the LED on (with VCC = 5V). transistors with integrated gate resistors do exist, but are rare and expensive, a simpler/cheaper solution would be to use a FET, like a 2N7000 no extra resistor needed. Remember only to use a FET that t...
by PiGraham
Wed Aug 01, 2018 6:33 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

stmulligan wrote:
Wed Aug 01, 2018 6:22 pm
My plan was one pin/one LED per GPIO. Seems I'm back where I started - not sure whether or not to try and drive this bar from GPIO.
You are 100% safe using 3.3V to Vcc.
by PiGraham
Wed Aug 01, 2018 6:28 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

You shouldn't connect 5V to gpio but here the LEDs will drop at least 1.7V so the gpio will not see more than 5 - 1.7 = 3.3V when the output is off so that should be OK. When the LED is on the pin voltage will be close to zero, of course. Use 3.3V if that works for you or use 5V if needed. Well I'm...
by PiGraham
Wed Aug 01, 2018 3:07 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

drgeoff wrote:
Wed Aug 01, 2018 2:42 pm
8 LEDs = 24 mA. total maximum.
Could be, although 24mA seems more likely to be the max rating of a single LED
by PiGraham
Wed Aug 01, 2018 3:05 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

Yes, they light fine by grounding the individual S pins, but I was told that using GPIO pins to ground devices is not a good idea (hence the topic title). By backwards logic, I meant that my original design drove 4 LEDs by setting a GPIO pin high to the already grounded LED. This inverts that logic...
by PiGraham
Wed Aug 01, 2018 1:58 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

That board looks likes this https://www.ebay.co.uk/itm/24mA-8Pcs-LED-Bar-Marquee-Display-Module-With-4-Kinds-of-Color-for-Arduino-RH/292651566302?hash=item44236484de:g:86wAAOSwUC1bVUlY That says 24mA 5V Assuming 2V forward voltage across each LED that implies 125R series resistors. (5V - 2V)/24mA = ...
by PiGraham
Wed Aug 01, 2018 1:46 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

Yes, I have no problem wiring up individual LEDs. My issue is that I'm moving from breadboards to field units. I need to make about 50 and they each have 4 LEDs. That's a lot of soldering so I bought a handful of these LED Bars. http://powerchalk.info/wp-content/uploads/2018/08/ledbar.jpg Only to r...
by PiGraham
Wed Aug 01, 2018 12:24 pm
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

From my readings, I assume that I need an NPN transistor - meaning I send low power to the base to supply ground to the LED. Can someone point to a suitable part# or ebay listing with a built in resistor on the base pin? I'm assuming the resistor needs to be 10K. You can drive small LEDs directly. ...
by PiGraham
Wed Aug 01, 2018 12:13 pm
Forum: Assistive technology and accessibility
Topic: Can a Pi be used in some way to prevent Dementia sufferers making landline calls to a specific number?
Replies: 15
Views: 498

Re: Can a Pi be used in some way to prevent Dementia sufferers making landline calls to a specific number?

Check out phones with parental controls. The BT600 is one that may help. It looks like it can block specific numbers as well as classes of number. You might be able to implement call blocking using PBX software such as Asterisk or openpbx and you may be able to connect that up to your landline and s...
by PiGraham
Wed Aug 01, 2018 9:20 am
Forum: Other projects
Topic: TCS34725 RGB sensor
Replies: 8
Views: 624

Re: TCS34725 RGB sensor

Can we get a number for yellow colour, like the Red, green and blue so we can plot a graph of it? Yellow will give a signal on red AND green. You could graph yellow calculating some combination of RGB. One approach is to convert RGB values to HSI (Hue, saturation, intensity, aka HSV). You could the...
by PiGraham
Wed Aug 01, 2018 9:03 am
Forum: General discussion
Topic: GPIO as GND
Replies: 47
Views: 802

Re: GPIO as GND

I know that LOW in Pi terms is the absence of voltage - not ground. So how would i control the four LED with four GPIO pins. I've tried grounding the VCC pin hoping they would share the ground and I could send 5v to the individual pins when needed, but the circuit (and the built-in resisters) are d...
by PiGraham
Wed Aug 01, 2018 7:42 am
Forum: Troubleshooting
Topic: help with H bridge for latching solenoid
Replies: 3
Views: 95

Re: help with H bridge for latching solenoid

I've grounded ISEN because I didn't think current regulation mode was needed; per the documentation: "High-current ground path. If using current regulation, connect ISEN to a resistor (low-value, high-power-rating) to ground. If not using current regulation, connect ISEN directly to ground." Fair e...
by PiGraham
Tue Jul 31, 2018 1:13 pm
Forum: Troubleshooting
Topic: help with H bridge for latching solenoid
Replies: 3
Views: 95

Re: help with H bridge for latching solenoid

Why have you grounded ISEN? Looking at the data sheet it seems that is a current sense pin that should have a sense resistor to ground. I'm not clear how that might prevent voltage appearing on the outputs but there are various protection modes. Check the data sheet and ensure you are using the devi...
by PiGraham
Tue Jul 31, 2018 8:23 am
Forum: Networking and servers
Topic: UDP using MAC addresses
Replies: 4
Views: 140

Re: UDP using MAC addresses

Hi! I'm looking for establishing an UDP connection using the IP address, the port and additionally the MAC address . Does anyone know how to do so using socket-handler library? Or another library. Thanks in advance! What are you trying to do? Use MAC address to route your message or limit the messa...
by PiGraham
Mon Jul 23, 2018 7:13 am
Forum: General discussion
Topic: Is it suitable? For a Computer Science course?
Replies: 44
Views: 1671

Re: Is it suitable? For a Computer Science course?

Imperf3kt wrote:
Sun Jul 22, 2018 10:05 pm

I'm not saying the Pi won't help him learn, but I am saying it is going to be useless for the coursework.
I think that is a valid concern, but it very much depends on the details of the coursework. A Pi might be ideal for some coursework and useless for other coursework.
by PiGraham
Sun Jul 22, 2018 3:07 pm
Forum: General discussion
Topic: Is it suitable? For a Computer Science course?
Replies: 44
Views: 1671

Re: Is it suitable? For a Computer Science course?

My son will be attending a Computer science course at uni in Sepetmber...would this be a useful thing to get in order to get him started in Computer science? If you are simply asking if comp sci students can get something out of having a Raspberry Pi then yes, absolutely. Get one! If you are asking...
by PiGraham
Thu Jul 19, 2018 10:00 pm
Forum: Graphics, sound and multimedia
Topic: * SIMULTANEOUSLY RECORD 2 VIDEOS *
Replies: 6
Views: 262

Re: * SIMULTANEOUSLY RECORD 2 VIDEOS *

I was only offering the basic concept as a starting point / interpretation of what the OP was seeking to do.
I sounds from what you say that it might be viable, using different tools. Two independent H264 compressed video streams could be multiplexed into a single vide file?
by PiGraham
Thu Jul 19, 2018 9:30 am
Forum: Graphics, sound and multimedia
Topic: * SIMULTANEOUSLY RECORD 2 VIDEOS *
Replies: 6
Views: 262

Re: * SIMULTANEOUSLY RECORD 2 VIDEOS *

Here's a suggestion for mux of two video streams Here is a simple (working) setup using gst-launch (install the gstreamer-tools package on Ubuntu/Debian): gst-launch v4l2src device=/dev/video1 ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=640, height=480 ! videobox border-alpha=0 left=-64...
by PiGraham
Thu Jul 19, 2018 8:58 am
Forum: Graphics, sound and multimedia
Topic: * SIMULTANEOUSLY RECORD 2 VIDEOS *
Replies: 6
Views: 262

Re: * SIMULTANEOUSLY RECORD 2 VIDEOS *

You may be able to multiplex two video streams into one file. That is typically how video and audio are combined in a file. Blocks of one data stream are interleaved or "multiplexed" with blocks of data for the other stream. You might be able to create a graph for gstreamer that does it. You could u...
by PiGraham
Thu Jul 19, 2018 8:39 am
Forum: Troubleshooting
Topic: 'Extending' USB - not working
Replies: 7
Views: 273

Re: 'Extending' USB - not working

You must run D+/- as twisted pair. Use actual USB cable. If you don't you alter the impedance and signal properties and that could easily make it not work as a USB connection. Routing USB through pin headers is not recommended for the sme reason but you might get away with it. USB connectors are des...
by PiGraham
Thu Jul 19, 2018 7:59 am
Forum: General programming discussion
Topic: What Does Hiding the Details of I/O in Library Calls Teach?
Replies: 63
Views: 2065

Re: What Does Hiding the Details of I/O in Library Calls Teach?

rpdom wrote:
Thu Jul 19, 2018 7:05 am
bensimmo wrote:
Thu Jul 19, 2018 6:32 am
That's when you get Orangutans.
In the library?
In the APE API?
by PiGraham
Wed Jul 18, 2018 5:38 pm
Forum: General programming discussion
Topic: What Does Hiding the Details of I/O in Library Calls Teach?
Replies: 63
Views: 2065

Re: What Does Hiding the Details of I/O in Library Calls Teach?

The whole idea of programming languages and symbolic instructions is obviously holding everyone back. Kids should be learning about computers by setting register load values on banks of switches. To be fair I can see benefits in kids learning about discrete logic circuits, how an adder can be made f...
by PiGraham
Wed Jul 18, 2018 5:29 pm
Forum: General programming discussion
Topic: What Does Hiding the Details of I/O in Library Calls Teach?
Replies: 63
Views: 2065

Re: What Does Hiding the Details of I/O in Library Calls Teach?

Of course the second one chooses Python to tackle a problem one has given up all hope of small size and performance. You can say that again. I rewrote a python program (it reads a BMP180 using the /sys interface and writes SQLite3 every three minutes) in C++ and the working set of the program goes ...

Go to advanced search