Go to advanced search

by IanS
Fri Oct 13, 2017 12:23 pm
Forum: Advanced users
Topic: Key system for IoT device
Replies: 7
Views: 1543

Re: Key system for IoT device

It sounds like you are looking for what is often called mutual authentication. Normally when using HTTPS, the server presents a certificate to the client to prove who it is. With mutual authentication, the client also has to prove who it is to the server, again often using a certificate based method...
by IanS
Tue Oct 10, 2017 2:25 pm
Forum: Networking and servers
Topic: General server security question.
Replies: 13
Views: 3154

Re: General server security question.

You may have nothing of value or interest on the exposed Pi, but that should not be your main concern. Consider what else a hacker can reach on your network once they have a foothold via the Pi. Having the Pi linked to the internet for only an hour every few days is no defence either. Some years ago...
by IanS
Thu Oct 05, 2017 10:18 am
Forum: Networking and servers
Topic: General server security question.
Replies: 13
Views: 3154

Re: General server security question.

You can put iptables rules in that 1) allow the local network to connect to the Pi, either using any protocol or locking it down further to specific protocols, 2) allow the PI to talk to anywhere, local or internet, 3) allow the outside world to talk to the Pi only on the required protocol(s), 4) bl...
by IanS
Fri Sep 29, 2017 9:26 am
Forum: Other projects
Topic: How to measure temperature of a Rasberry pi?
Replies: 10
Views: 6516

Re: How to measure temperature of a Rasberry pi?

Having just run the following scripts (and with the vcgencmd method) , it would appear that running the command does not cause enough of a temperature increase to be noticeable above the low granularity of the measurement. Run quickly: for i in {1..10} do cat /sys/devices/virtual/thermal/thermal_zon...
by IanS
Wed Sep 27, 2017 12:49 pm
Forum: Automation, sensing and robotics
Topic: Raspi + L298N = Hang
Replies: 4
Views: 961

Re: Raspi + L298N = Hang

Some L298N boards have a voltage regulator that lets you supply the logic 5V from the motor power supply. It is normally switchable. If your board has one, check it is turned off, or disconnect the Pi from the L298N 5V supply. You will still need to use a ground connection. I have had strange result...
by IanS
Fri Sep 22, 2017 9:36 am
Forum: Advanced users
Topic: Acceleration and Impact Sensing with the Pi 3
Replies: 4
Views: 1576

Re: Acceleration and Impact Sensing with the Pi 3

I am not familiar with the Teensy platform, but for high speed data capture where you want the sample time to stay regular I would seriously consider using a dedicated microprocessor like an arduino over a general purpose computer like a Pi. The problem with the Pi is that tasks running in the backg...
by IanS
Thu Sep 21, 2017 4:24 pm
Forum: Advanced users
Topic: Acceleration and Impact Sensing with the Pi 3
Replies: 4
Views: 1576

Re: Acceleration and Impact Sensing with the Pi 3

There are a number of guides on converting to a read-only file structure for the Pi. How about following one of those so that data transfer to or from the SD is minimised, and trying to fasten the card in as best you can too. A Pi3 where the card needs to be pulled straight out is probably better th...
by IanS
Fri Sep 15, 2017 3:34 pm
Forum: Networking and servers
Topic: Cluster / Bramble networking method or software?
Replies: 6
Views: 1447

Re: Cluster / Bramble networking method or software?

I am afraid I am not familiar with setting up MQTT - I tend to work at the raw sockets end instead. However, judging by the number of posts on the subject, many people have had success with using Mosquito as a Pi based broker, although if you are still on the Jessie distribution it has an older vers...
by IanS
Fri Sep 15, 2017 3:19 pm
Forum: Networking and servers
Topic: ssh to my home pi through 3G
Replies: 6
Views: 3798

Re: ssh to my home pi through 3G

Have you checked that your ppp0 address is internet routable? Check what it is now, as it will change occasionally, then try a connection from elsewhere - a real ssh connection or even just a ping - perhaps from a ssh or network diagnostic app on a smartphone, but not from anything connected via the...
by IanS
Thu Sep 14, 2017 4:42 pm
Forum: Networking and servers
Topic: Cluster / Bramble networking method or software?
Replies: 6
Views: 1447

Re: Cluster / Bramble networking method or software?

How to go about this depends on what balance you are looking for between speed and reliability. For maximum speed you well need to work at a raw socket level, but it is much easier (and probably still fast enough) to use a messaging protocol designed for handling sensor information, such as MQTT. Th...
by IanS
Thu Sep 14, 2017 9:01 am
Forum: Other projects
Topic: Another space bound Pi?
Replies: 0
Views: 363

Another space bound Pi?

It looks like a couple of researchers have designed a cheap and efficient means of communicating with cubesats. The smallest form factor for these, which is being used here, are only 10cm cubes, so they have no room for large antennae. Their design uses the PV panels as receivers, but this requires ...
by IanS
Fri Sep 08, 2017 9:51 am
Forum: Automation, sensing and robotics
Topic: Make stepper motor faster
Replies: 9
Views: 9478

Re: Make stepper motor faster

For anything larger than a little 28BYJ-48 you will need to use a chopper driver board (e.g. A4988 or DRV8825) and a higher voltage supply. You cannot drive it properly from the Pi. If you look at the spec sheet for a medium NEMA17 motor it will normally say something like current limit 1A, winding ...
by IanS
Fri Sep 08, 2017 9:41 am
Forum: Automation, sensing and robotics
Topic: Line Follower Sensor
Replies: 5
Views: 1229

Re: Line Follower Sensor

None of them seem to have anything to adjust the sensitivity. The third one might, but I read the description as saying only the forward (collision detection) sensor is variable. This means the only way to adjust the sensor is by varying the height, so you have to allow for a mechanical means of doi...
by IanS
Fri Sep 08, 2017 9:31 am
Forum: Automation, sensing and robotics
Topic: Stepper motor control using Pi
Replies: 14
Views: 16116

Re: Stepper motor control using Pi

I have a similar size motor (NEMA 17, 1.7A), but without the attached gearbox, which I drive successfully from a DRV8825. Check the driver board data sheet to find out what value sense resistor is used to check the current. The DRV8825 chip data sheet gives the formula for the reference voltage. If ...
by IanS
Mon Sep 04, 2017 9:34 am
Forum: Graphics, sound and multimedia
Topic: need help to make a sound accelerator
Replies: 1
Views: 549

Re: need help to make a sound accelerator

If all you need is to take a set of sound samples and alter the pitch that they are played at in response to some input then google 'Raspberry Pi pitch shifter' and you will find a number of examples on how this can be done.
by IanS
Mon Aug 28, 2017 9:19 pm
Forum: Automation, sensing and robotics
Topic: Make stepper motor faster
Replies: 9
Views: 9478

Re: Make stepper motor faster

I've been playing with a NEMA17 motor today, trying to find what kind of speeds and accelerations it supports under a moderate load. The motor is a 17HD48002H-22B, available easily through eBay or Amazon ( https://www.amazon.co.uk/Quimat-Stepper-Bipolar-Connector-Mounting/dp/B06XQWMDWT/ref=sr_1_3?ie...
by IanS
Mon Jul 24, 2017 7:50 am
Forum: Automation, sensing and robotics
Topic: Multiple HC-SR04 Ultrasonic Sensors
Replies: 5
Views: 8104

Re: Multiple HC-SR04 Ultrasonic Sensors

If you cycle through the sensors rather than trying to use them simultaneously then there will be no problem with incorrectly received echoes. They have a range of about 2m, so 4m (there and back) at 330m/s is 12ms. Allow double this for good measure, so check one sensor every 25ms.
by IanS
Wed Jul 19, 2017 9:06 pm
Forum: Automation, sensing and robotics
Topic: Multiple HC-SR04 Ultrasonic Sensors
Replies: 5
Views: 8104

Re: Multiple HC-SR04 Ultrasonic Sensors

You can use a common power and ground link between the sensors, but beware of how much current you are trying to draw if you use a large number of sensors. Normally each sensor would also require two GPIO pins, for pulse trigger and echo in, but it is possible to use a single pin. Take a look at htt...
by IanS
Wed Jul 19, 2017 8:53 pm
Forum: Automation, sensing and robotics
Topic: OK to remove power LED
Replies: 9
Views: 2122

Re: OK to remove power LED

Even easier: use a 5V LED (with integrated resistor) between GPIO14/TXD0 (Pin 8) and ground. That's it, as long as serial console is enabled. It used to be on by default, but may not be any more - see https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=159023&p=1034303 . I have a couple of boxes...
by IanS
Thu Jul 13, 2017 10:23 am
Forum: Networking and servers
Topic: Network monitoring using PI
Replies: 4
Views: 5829

Re: Network monitoring using PI

You also need to be aware of the difference between a hub and a switch. Hubs receive a packet from one port and send it out to all other ports. Switches learn which MAC address is connected to which port, so only send packets out to the necessary port. Hence something listening on one port may not s...
by IanS
Wed Jul 12, 2017 9:43 am
Forum: Automation, sensing and robotics
Topic: High torque motor for pulley system
Replies: 7
Views: 3126

Re: High torque motor for pulley system

Just because a worm drive is good at resisting being back driven does not mean that the strong forces are not there. If you try and hold the gears in place with a lightweight wooden frame you may find that the frame just gets ripped apart. Go for a motor with an integrated gearbox, then build a fram...
by IanS
Tue Jul 11, 2017 1:33 pm
Forum: Automation, sensing and robotics
Topic: High torque motor for pulley system
Replies: 7
Views: 3126

Re: High torque motor for pulley system

You need to look at the torque for the motor when running, and also when stationary. For example http://www.robotshop.com/uk/dfrobot-6v-180-rpm-micro-dc-geared-motor-with-back-shaft.html , which is a motor and gearbox combo of a type common in small model vehicles, has a stall torque of just of 11oz...
by IanS
Mon Jul 03, 2017 8:41 am
Forum: Other projects
Topic: Raising bed to ceiling. need motor advice..
Replies: 22
Views: 4554

Re: Raising bed to ceiling. need motor advice..

One final possibility, purely structural with no IT element. When I was that sort of age, and up to 16, my room was reasonably small too; about 9'x6' I think. Hence, no room for a permanent desk. I ended up with a fold out desk - just a board with lockable hinges like http://www.springfieldgrp.com/p...
by IanS
Thu Jun 29, 2017 3:23 pm
Forum: Other projects
Topic: Raising bed to ceiling. need motor advice..
Replies: 22
Views: 4554

Re: Raising bed to ceiling. need motor advice..

It really might be easier to go for a raised or loft bed with room for a desk / guest bed underneath, such as https://s-media-cache-ak0.pinimg.com/originals/a7/f5/9d/a7f59d013be27bb263afe0d757219a98.jpg . You can get them with the bed at various heights. My 5yo son has one very similar to this (but ...
by IanS
Tue Jun 27, 2017 4:34 pm
Forum: Other projects
Topic: Raising bed to ceiling. need motor advice..
Replies: 22
Views: 4554

Re: Raising bed to ceiling. need motor advice..

That motor looks too small. It is quoted as 160RPM, 350oz-in, 6mm shaft (nice mix of imperial and metric measurements just to keep you awake). Obviously you will not be able to wrap the lifting wire around that small shaft, but will need to put some kind of wheel or drum on. You could go for a coupl...

Go to advanced search