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by mjtessmer
Wed Apr 19, 2017 7:11 pm
Forum: Off topic discussion
Topic: SN74LS189 Replacement/Equivalent
Replies: 4
Views: 2820

Re: SN74LS189 Replacement/Equivalent

I saw tthem at Anchor Electronics in Santa Clara California for $3.65 each.
You might want to consider using a larger, more current static RAM. Just
tie unused address inputs low.
by mjtessmer
Tue Dec 13, 2016 1:37 am
Forum: Off topic discussion
Topic: Heart Rate monitor chip Cheaper (barely) than a Pi Zero...
Replies: 9
Views: 2154

Re: Heart Rate monitor chip Cheaper (barely) than a Pi Zero.

There is another alternative to measuring heart rate; pulse oximeter. It can also measure
percentage of oxygen in the blood. Cost as low as $11.59.
by mjtessmer
Wed Mar 23, 2016 10:17 pm
Forum: Off topic discussion
Topic: Connecting a NPN Photoelectric light sensor
Replies: 4
Views: 898

Re: Connecting a NPN Photoelectric light sensor

So, if I understand this correctly, I need to get a relay with a coil voltage that works with the 10-30V power input of the sensor, and then connect the 3.3V supply of the RPi to a GPIO pin through the contacts of the relay? Yes that is one alternative; common relay coil voltage is 12V, so you coul...
by mjtessmer
Tue Mar 22, 2016 6:33 pm
Forum: Off topic discussion
Topic: Connecting a NPN Photoelectric light sensor
Replies: 4
Views: 898

Re: Connecting a NPN Photoelectric light sensor

Brown is the Positive Power Input Blue is the Negative Power Input(GND) White is the Light-on/Dark-on Select Input Black is a Open Collector Output to a Relay Coil; the other side of the Relay Coil going to Positive Power Input. Alternatively you could use and opto-isolator (with current limiting re...
by mjtessmer
Fri Apr 10, 2015 3:23 am
Forum: Off topic discussion
Topic: Interesting little board:CodeBug
Replies: 58
Views: 7076

Re: Interesting little board:CodeBug

Found a third "bug", called BBC Bug
http://bug.iotoy.org/bug

This one is even more vague.
by mjtessmer
Sat Sep 20, 2014 5:19 pm
Forum: Off topic discussion
Topic: How do I get computer electronic parts?
Replies: 7
Views: 1291

Re: How do I get computer electronic parts?

Have you tried Tayda Electronics
http://www.taydaelectronics.com/
by mjtessmer
Tue Jul 08, 2014 9:59 pm
Forum: Off topic discussion
Topic: Where do you buy components for your projects?
Replies: 11
Views: 2634

Re: Where do you buy components for your projects?

If shipping time is of low concern try Tayda Electronics
http://www.taydaelectronics.com/
by mjtessmer
Sun Jul 06, 2014 1:16 pm
Forum: Off topic discussion
Topic: My new board (With better pictures)
Replies: 57
Views: 16424

Re: My new board

If there is a serial controller on the board, look for some MC1488's and MC1489's (TTL to RS232 level converters). You do not need a "multibus computer", just need a 86pin connector to provide power.
by mjtessmer
Fri Jul 04, 2014 3:36 am
Forum: Off topic discussion
Topic: My new board (With better pictures)
Replies: 57
Views: 16424

Re: My new board

Can you post better pictures of the board? (Top and bottom)
Does the board have any video IC's? Try powering up board.
by mjtessmer
Thu Jun 26, 2014 12:38 am
Forum: Off topic discussion
Topic: My new board (With better pictures)
Replies: 57
Views: 16424

Re: My new board

It fits in a Intel Multibus card slot. The two blue connectors on the
card are iSBX slots.
by mjtessmer
Tue Mar 26, 2013 10:53 pm
Forum: Off topic discussion
Topic: Where to get cheap electronic components?
Replies: 11
Views: 6647

Re: Where to get cheap electronic components?

I have used Futurlec with success: www.futurlec.com
Another good source is Tayda Electronics: www.taydaelectronics.com
by mjtessmer
Thu Jan 03, 2013 6:30 pm
Forum: Add-ons
Topic: GPIO Board development
Replies: 11
Views: 3700

Re: GPIO Board development

I have a question about the power supply circuit section.
Is the USB1 connector a power in or power out?
If USB1 is power in, I suggest an in-line diode going from
the USB V+ to the 4.3 volt.
by mjtessmer
Tue Aug 21, 2012 9:45 pm
Forum: Add-ons
Topic: EMBIR-JX
Replies: 45
Views: 28881

Re: EMBIR-JX

I am not following your math. I thought each chip can only do 16 I/O's. 5 IC's
* 16 gives 80 I/O's?? Am I missing some thing?

I thought that 5 Boards (with 2 chips each) would give 160 I/Os.
by mjtessmer
Thu Aug 16, 2012 12:31 am
Forum: Add-ons
Topic: Is 3V3 GPIO HIGH voltage enough to fully turn on ULN2803a?
Replies: 7
Views: 3208

Re: Is 3V3 GPIO HIGH voltage enough to fully turn on ULN2803

You are not missing anything. Transistors are current amplifiers.
Collector current equals hfe(current gain) * base current.
Base current is determined by voltage input divided by base
resistance (which is approx 10k ohms).
by mjtessmer
Mon Jul 09, 2012 3:51 am
Forum: Add-ons
Topic: EMBIR-JX
Replies: 45
Views: 28881

Re: EMBIR-JX

Could you post a large high-resolution photo of the top side of the board and if there any components on the bottom side? It would help to determine what chips you are using. I assumed, that when you started your project, you created some block diagram of what chips you planned to use and how they w...
by mjtessmer
Mon Jul 02, 2012 2:59 am
Forum: Other projects
Topic: The MagPi Magazine www.themagpi.com
Replies: 253
Views: 45245

Re: The MagPi Magazine www.themagpi.com

Scroll to the top of the page. Copy and paste the URL.
by mjtessmer
Thu Jun 28, 2012 2:30 am
Forum: Add-ons
Topic: EMBIR-JX
Replies: 45
Views: 28881

Re: EMBIR-JX

Will you make a block diagram or schematic available?
by mjtessmer
Sat May 12, 2012 1:06 am
Forum: Teaching and learning resources
Topic: Broadcom documentation
Replies: 8
Views: 4648

Re: Broadcom documentation

<t>I did save them to a new folder and opened the index<br/> <br/> file; but it did not display properly.  I had to open each<br/> <br/> individual file on the web, then copy the text contents to<br/> <br/> a text editor, then re-save to a ".html" file.  I did notice that<br/> <br/> the new files we...
by mjtessmer
Fri May 11, 2012 8:47 pm
Forum: Teaching and learning resources
Topic: Broadcom documentation
Replies: 8
Views: 4648

Re: Broadcom documentation

When I click on the "index.html" file I get

the source text of the above file.  How do

I display the regular html output?
by mjtessmer
Mon Apr 30, 2012 7:05 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Pi and Arduino
Replies: 24
Views: 8043

Re: Pi and Arduino

<t>rmm200 said: <br/> <br/> <br/> Three additional wires from Pi to Arduino (gnd, Snd, Rcv). I don't think level shifting required - this is not RS232. Different drivers on each end; should be transparent to user. Different device IDs.<br/> <br/> <br/> <br/> The standard Arduino's serial port is 0-5...
by mjtessmer
Tue Apr 24, 2012 4:15 am
Forum: General discussion
Topic: We've just released the schematics!
Replies: 34
Views: 5176

Re: We've just released the schematics!

Thanks! Andrew

Gert:  Can you tell us which pins the I2S signals are on?
by mjtessmer
Sat Apr 21, 2012 12:56 am
Forum: General discussion
Topic: We've just released the schematics!
Replies: 34
Views: 5176

Re: We've just released the schematics!

Would it be possible to release a pinout and block diagram of the

BCM2835 SOC?
by mjtessmer
Sun Apr 01, 2012 3:47 pm
Forum: General discussion
Topic: proposing a name for R-PI expansion boards.
Replies: 28
Views: 4012

Re: proposing a name for R-PI expansion boards.

Did you mean "leafs"?
by mjtessmer
Sat Mar 03, 2012 5:57 pm
Forum: General discussion
Topic: Listing of Fedora apps are "lite enough" for the RPi?
Replies: 14
Views: 3354

Re: Listing of Fedora apps are "lite enough" for the RPi?

The developer of Puppy Linux is working on a port

to the RaspberryPi.
by mjtessmer
Sun Jan 01, 2012 11:14 pm
Forum: Other projects
Topic: GPIO -> Multiple Serial Ports (UART)
Replies: 25
Views: 42791

Re: GPIO -> Multiple Serial Ports (UART)

Maxim has a SPI to UART/RS232 converter chip; MAX3111.

You can hook up several of these chips to the R-Pi's

SPI port on the GPIO connector and then use the GPIO bits

to select the chips.

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