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by mikronauts
Mon Jul 24, 2017 8:30 pm
Forum: Beginners
Topic: Using Rotary Encoder to measure the distance
Replies: 1
Views: 570

Re: Using Rotary Encoder to measure the distance

google 'python odometry'
by mikronauts
Wed Jul 19, 2017 3:18 pm
Forum: General discussion
Topic: Powering exteranl 3.3V device
Replies: 5
Views: 2044

Re: Powering exteranl 3.3V device

I've read that the original A/B had about 50mA of elbow room left from the on-board 3v3 regulator. Newer Pi's may allow more, however if the 3v3 regulator draws too much, the 5V can be pulled too low, leading to the dreaded lightning symbol indicating low voltage. How much you can draw depends on: -...
by mikronauts
Mon Jul 17, 2017 6:58 pm
Forum: Compute Module
Topic: Expandable baseboard (slot system) for CM3
Replies: 30
Views: 13982

Re: Expandable baseboard (slot system) for CM3

Imre, I am probably stating the obvious here... 1) You do realise the CM3's pins do not form a "bus" in computer terms? It would be possible to emulate one, but it would be painfully slow. 2) Multiple CM3's could form a cluster, but you would need to add Ethernet PHY's and an ethernet switch It woul...
by mikronauts
Sun Jul 16, 2017 4:19 pm
Forum: Beginners
Topic: help a noob control 8 motors and a sensor
Replies: 7
Views: 1296

Re: help a noob control 8 motors and a sensor

you need to figure out the mass of the objects you want to move before you can find the motors you need
by mikronauts
Wed Jul 12, 2017 5:56 pm
Forum: General discussion
Topic: Password Protect SD Card?
Replies: 20
Views: 4002

Re: Password Protect SD Card?

Google "usb protection dongle"
by mikronauts
Wed Jul 12, 2017 5:31 pm
Forum: General discussion
Topic: Password Protect SD Card?
Replies: 20
Views: 4002

Re: Password Protect SD Card?

Can't be done. Also would not protect against image copying. If you are worried about copying, add an appropriate USB key dongle. Thanks, I would like to password protect the sd card so someone can't plug the sd card into a computer and get the contents but if it is plugged in to a certain sd card i...
by mikronauts
Fri Jul 07, 2017 4:03 pm
Forum: General discussion
Topic: No more WDLabs?
Replies: 21
Views: 3854

Re: No more WDLabs?

Too bad.

I just received my PiDrive 375GB.
W. H. Heydt wrote:I have received an e-mail from WD Labs. The shutdown is not a rumor.
by mikronauts
Fri Jun 30, 2017 4:40 pm
Forum: Raspbian
Topic: PiBakery
Replies: 13
Views: 3875

Re: PiBakery

This looks like a nice project! Two requests: 1) Linux support - I don't run MacOS, and I run Windows as little as possible :) 2) Source tarball generation - have Pi bakery generate a shell script that would download all the sources for the Raspbian configuration that it generates, and have the scri...
by mikronauts
Fri Jun 30, 2017 4:31 pm
Forum: General discussion
Topic: Pi Zero now available in multiples !
Replies: 15
Views: 3335

Re: Pi Zero now available in multiples !

The one per customer of the bare unit has NOT been lifted.
mikerr wrote:With the lifting of the 1 per customer limit it now becomes a proper product IMO
by mikronauts
Sat Jun 24, 2017 12:41 am
Forum: Networking and servers
Topic: Running multiple pi's on a tractor
Replies: 26
Views: 4740

Re: Running multiple pi's on a tractor

Why on earth do you need 25 Pi3's? So basically I want to run about 25 raspberry pi 3's on my tractor to monitor some stuff using the camera. Electricity-wise, I'm concerned about the different voltages that may come out of the tractor at different revs. What would be the most suitable way to overco...
by mikronauts
Wed Jun 21, 2017 4:47 pm
Forum: Graphics, sound and multimedia
Topic: Using the pi 3 as a 16+ channel DSP
Replies: 6
Views: 3220

Re: Using the pi 3 as a 16+ channel DSP

It depends on what you want to do with all those I2S channels. I'd synchronise the Pi's with just one signal, possibly from a master, and transfer the data over Ethernet or USB, using a host to re-assemble/partition the channels - I would not even try to transfer the data between the Pi's over GPIO ...
by mikronauts
Tue Jun 20, 2017 10:57 pm
Forum: Graphics, sound and multimedia
Topic: Using the pi 3 as a 16+ channel DSP
Replies: 6
Views: 3220

Re: Using the pi 3 as a 16+ channel DSP

My friend, I have been doing hard real time I/O for ~30 years, on a lot of different micro controllers. It is a LOT more than a "custom driver". Frankly, I am not sure it is feasible at all, even at the lower clock rates. Simultaneously bit-banging 16 channels of I2S audio (8 in, 8 out) in software ...
by mikronauts
Tue Jun 20, 2017 5:32 pm
Forum: Graphics, sound and multimedia
Topic: Using the pi 3 as a 16+ channel DSP
Replies: 6
Views: 3220

Re: Using the pi 3 as a 16+ channel DSP

Good luck. Odds of getting it working in any reasonable amount of time are very low. Not impossible, but with that number of channels: 1) go bare metal 2) dedicate a core to inputs 3) dedicate another core to outputs The issue is jitter free timing. The 25MHz is not something guaranteed for all I/O ...
by mikronauts
Tue Jun 20, 2017 5:26 pm
Forum: Automation, sensing and robotics
Topic: RPi, MCP3008 and Pressure Transmitter
Replies: 2
Views: 701

Re: RPi, MCP3008 and Pressure Transmitter

As Joan said, the Pi's 3v3 is a reasonable voltage reference, however it can fluctuate under load, with the error being the exact 3v3 instantaneous voltage at the time the sample is taken. What kind of accuracy do you need? Even with a perfect 3v3 reference (which does not exist) you can only get 3....
by mikronauts
Wed Jun 14, 2017 4:48 pm
Forum: Automation, sensing and robotics
Topic: CamJamEDUKit 3 Motors go at different speeds
Replies: 6
Views: 1231

Re: CamJamEDUKit 3 Motors go at different speeds

I've seen +/- 25% different unloaded motor speeds with the cheap yellow gear motors, between motors from the same kit.

These days I measure the unloaded motor speeds of all motors on a bot and use PWM to get the speeds as close as is feasible.

My last two articles in SERVO talked about this.
by mikronauts
Fri Jun 09, 2017 4:44 pm
Forum: Automation, sensing and robotics
Topic: analog input interfacing
Replies: 15
Views: 4025

Re: analog input interfacing

You should get a commission! Btw, the reason (as I am sure you have guessed) that I keep harping on ground differential issues is that I've seen people in the past ignore them (run many sensors of different circuits feeding an ADC on yet another)... and then wonder why they are having problems. I wi...
by mikronauts
Thu Jun 08, 2017 6:07 pm
Forum: Automation, sensing and robotics
Topic: analog input interfacing
Replies: 15
Views: 4025

Re: analog input interfacing

Thanks - I like that board even more now! If and only if the 24V (pretty standard in industrial I/O) power supplies ground and the Pi's ground have no common mode issues (ie on the same circuit, grounds tied togeather, or transformer isolated with grounds tied togeather) it should work. Otherwise th...
by mikronauts
Wed Jun 07, 2017 5:00 pm
Forum: Official Foundation Display
Topic: Need to see more content on your 7in Touch display?
Replies: 11
Views: 10558

Re: Need to see more content on your 7in Touch display?

Also has aliasing issues when scaling down to the native panel resolution.

I have a cheap Win10 tablet with a 1024x600 display - but MS forces the mode to 1280x800, so everything is scaled & fuzzy.
by mikronauts
Wed Jun 07, 2017 4:58 pm
Forum: Automation, sensing and robotics
Topic: Relays and failsafe
Replies: 27
Views: 3901

Re: Relays and failsafe

I was thinking about using a shift register or counter as follows: - 555 timer generates pulses for counter,Pi keeps clearing the counter, otherwise final count "disconnects" relay control from the Pi via logic. (active low logic from Pi, NOT overflow OR'd with Pi's output fed to relay, overflow als...
by mikronauts
Wed Jun 07, 2017 4:50 pm
Forum: Automation, sensing and robotics
Topic: analog input interfacing
Replies: 15
Views: 4025

Re: analog input interfacing

That is a nice looking hat. Their use of 150R resistors suggests they are running the ADC at 3v3, and common mode voltage differences are likely an issue. I agree, using three Pi's and three hats (if common mode issues are not an issue) would be a good solution. to the OP: Unless you can avoid diffe...
by mikronauts
Tue Jun 06, 2017 11:35 pm
Forum: Automation, sensing and robotics
Topic: analog input interfacing
Replies: 15
Views: 4025

Re: analog input interfacing

Depends of how the 4-20mA sensors are powered. Theoretically, you can just use a 250 ohm resistor, and measure the voltage drop across it, assuming no common mode voltage issues. The problem is that most power supplies these days do not use a transformer, and unless the power supplies to the sensors...
by mikronauts
Mon Jun 05, 2017 2:42 pm
Forum: Automation, sensing and robotics
Topic: analog input interfacing
Replies: 15
Views: 4025

Re: analog input interfacing

You may find my article helpful:

http://www.mikronauts.com/raspberry-pi/ ... and-howto/
binyameen panali wrote:i am new to raspberry pi. i have a requirement that need to connect 20 analog input to raspberry pi3. how can approach to it. sir please give me a solution
by mikronauts
Mon Jun 05, 2017 2:41 pm
Forum: Automation, sensing and robotics
Topic: CamJam Edukit #3 - What is best to power the Pi?
Replies: 10
Views: 1817

Re: CamJam Edukit #3 - What is best to power the Pi?

I recommend using USB power banks with a 2A+ output, and 5000mAh+ capacity, and a 4xAA (or larger) battery pack for the motors. Here are a couple of my bots using such power: http://www.mikronauts.com/robot-zoo/elf-2wd-pi-robot/ http://www.mikronauts.com/robot-zoo/hobbit/ Ok, this isn't really a nas...
by mikronauts
Thu Jun 01, 2017 3:24 pm
Forum: Automation, sensing and robotics
Topic: Datalogging Energy Meter via MODBUS
Replies: 3
Views: 2863

Re: Datalogging Energy Meter via MODBUS

I've done a lot of work interfacing Modbus (and other) devices to PC's running HMI & SCADA packages. For pure monitoring/logging it is fairly safe to write your own logging software, as long as you don't saturate your comm bus, especially for a non-critical home application. This assumes that your P...
by mikronauts
Thu Jun 01, 2017 3:17 pm
Forum: Automation, sensing and robotics
Topic: Relays and failsafe
Replies: 27
Views: 3901

Re: Relays and failsafe

What you are looking for is a watchdog dimer + safety circuit. One way of implementing such a circuit (as you are driving the relays high) would be to use a dual input AND gate to drive each relay. For each relay, one input to its AND gate would be the current Pi GPIO, the other the output from a wa...

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