Show Posts
Pages: 1 2 [3] 4 5 ... 10
31  Using Arduino / Installation & Troubleshooting / Re: Ubuntu 12.04 unable to find /dev/ttyACM0 on: October 28, 2012, 03:35:30 pm
I added username to dialout then plugged UNO in. It was recognised and reported on /dev/ttyACM. Tried to upload - error message.

Disconnected without closing Arduino interface, reconnected and upload successful. Fails on serial console sometimes.

32  Using Arduino / Project Guidance / Re: LED light detector- two states - blink and steady on: October 25, 2012, 09:27:22 pm
The TEMT6000 is sensitive and easy to use.

The LED blinking produces a lower average analog input, with steady and off, the high and low. I think it's just a matter of writing a sketch to calculate the average voltage of the flashing LED, giving 3 states to work with for hardware control.

LED during capture is on/off per second, which is quite slow. Sampling sensor inputs over several seconds, adding and averaging should establish the 3 states of operation. No doubt there will be slight variation in sensor values. Perhaps calibration or a range for high and mean values.
33  Using Arduino / Project Guidance / LED light detector- two states - blink and steady on: October 25, 2012, 07:12:21 pm
I am thinking of using an LED as a light detector to detect illumination of another LED, which indicates operation of an astro CCD camera in three states.

LED off - no operation
LED blinks - operating (taking a picture)
LED steady downloading image to PC - not taking picture.

The states that I need to differentiate are blinking and steady; that is

LED blinking Arduino do nothing.
LED steady, Arduino operate ancillary equipment.

That is, differentiating fluctuating and steady analog input.

Is this a feasible approach? Would blink rate - sampling the analog input be a restriction.
34  Using Arduino / Project Guidance / Re: Astro sector drive - tilt sensors - accelerometers - GPS - compass on: October 21, 2012, 11:47:58 pm
Quote
Why not just use an equatorial mount and just one motor?

To avoid the need for an optical alignment scope and much quicker, theoretically.

Quote
Like all the best geek projects, I expect you would spend more time creating an automated setup than you would ever have spent doing it manually. That's not a reason not to do it, of course.

 smiley That's what I'm afraid of and my experience to date... Fortunately this project can be built in stages - functional from the start.

Will an encoder/GPS work in this configuration - a quadrant? I think the '0' end point would have to be calibrated at each set up, after leveling the device. Which might be simpler and more accurate than a graduated scale.

The stepper motor is one of those geared 1/64, 64 step 28Yxx 5v steppers of which there are thousands on ebay.
35  Using Arduino / Project Guidance / Astro sector drive - tilt sensors - accelerometers - GPS - compass on: October 21, 2012, 04:59:33 pm
I am thinking about building a sector drive to track and photograph the night sky - long exposures. The unit will sit on a rotating level platform and align itself to N/S and set the latitude of the right ascension axis automatically. Leveling could also be automatic, but that's not essential.

The plan is to achieve North - South alignment and latitude setting by reference to an electronic compass (GPS?). The compass will operate on a level platform - no tilt issues. Latitude setting, derived from a GPS module, will be from 0 - 90 (North/South is irrelevant). The tracking drive will be static - that is, no electronic control, just relying on predetermined radii of the sector arm and drive pully/gear/friction drive.

I have looked at tilt sensors and accelerometers, GPS modules and compasses. I am a little confused about whether I should use a tilt sensor to measure the latitude setting of the unit - related to the GPS position, or an accelerometer. Furthermore, how accurate are electronic compasses - is a few arc seconds asking too much?

This will be my 5th Arduino project.


36  Using Arduino / General Electronics / Re: Heating Nichrome wire - power, current, voltage requirements? on: March 25, 2012, 07:57:22 pm
Thanks Mark. Actually, it's 0.25R. I worked the numbers again and realised that I had misread the tables at Wikipedia.
37  Using Arduino / General Electronics / Re: Heating Nichrome wire - power, current, voltage requirements? on: March 25, 2012, 07:22:47 pm
Yes, but it's negligible in the desired temperature range ~20C.

To raise temperature of the wire by 20C requires 0.5A and guess a linear amp/heating scale is probably close enough for this application.

The basic circuit will be an11R, in series with the Nichrome element and +12v supply. PWM the voltage through a logic level n-channel MOSFET Gate, -ve side of heating element to Drain and Source to GND. This gives ~1amp to play with, but I need to calculate the requirements for raising the temperature of the glass. A variable resistor in place of the 11R will provide more power flexibility.
38  Using Arduino / General Electronics / Re: Heating Nichrome wire - power, current, voltage requirements? on: March 25, 2012, 02:30:13 pm
Thanks. It's 0.25R ((1.0015R/foot of wire @ 20C)/4 =~0.25R for 3 inches).

Intuitively, this seems like too little power. I want to be sure that these calculations are ball park.





39  Using Arduino / General Electronics / Heating Nichrome wire - power, current, voltage requirements? on: March 24, 2012, 10:47:07 pm
Hi. I want to calculate the energy requirements and temperature increase of 3 inches (75mm) of 22AWG Nichrome wire.

Referring here. 3" of 22AWG Nichrome, requires approx 0.5 amps to increase its temperature by 20C (68F). The resistance through the wire is ~0.25R, and increase in R due to heating up to 20C very small - assuming zero.

E = IR
E = 0.5*0.25= 0.125v, is the voltage required to provide 0.5amps to a wire with a resistance of 0.25R and heat it 20C (68F) from 0C (32F). In which case given the very small R values in question, raising the temperature of the wire by 20C from any other temperature state, will require the same current and voltage.

P = IE
P = 0.5*0.125 = 0.0625 Joules 0.0625watts.

It makes sense that the energy required to heat 3" of 22AWG wire will be quite small. I'm wondering if my calculations are correct? Not included, is the additional energy to warm a small flat glass component, 22mm x 15mm x 0.8mm to which the Nichrome will be attached.

The plan is to schedule power using PWM switching a logic level mosfet.
40  Using Arduino / General Electronics / Re: mosfet switching on: January 22, 2012, 05:22:01 pm
I think the offending part is a terminal block with connector receptacles. I used a jumper to bridge the TEC -ve and digital ground - PCB on the drawing board.
41  Using Arduino / General Electronics / Re: mosfet switching on: January 21, 2012, 06:13:22 pm
That's correct - separated the lines to ground - analog and digital to the Arduino board.

Unfortunately, the solution of connecting to the 'analog ground' reintroduced noise from the MOSFET/TEC switching, but I fixed that with 22uf gate to source.

In hindsight I agree that connecting to the dedicated analog ground wire bypassed an otherwise poor connection on the 'digital ground'.

Well, this has been an experience. I will retrace the wiring see what gives.
42  Using Arduino / General Electronics / Re: mosfet switching on: January 20, 2012, 08:08:37 pm
Thanks folks.

I found the fault, which I thought I had fixed - obscure, to me at least.

Two paths to GND - analog and digital - both are tied to the board. However, it was necessary to tie FET source to GND through the analog GND, as well as the GND shared by digital functions and power supply.

Pull down resistor is doing it's job now.

Thanks for the advice. Now to improve the code.
43  Using Arduino / General Electronics / Re: mosfet switching on: January 19, 2012, 01:28:44 pm
I have the power supply caps in place and find that the FET gate is not going to 0. Resistors of different values gate to ground is the only means of temperature control. Basically, the gate is on constantly, irrespective of pwm or digital pin 0 value.

I have reproduced the circuit on Every Circuit, an Android app, and clearly see the effect of different resistor values.

An alternative is to use another FET. The previous Fairchild chip worked every time but the power rating was too low and rds on a bit too high. I want to avoid another layer of complexity if I can.
44  Using Arduino / General Electronics / Re: mosfet switching on: January 18, 2012, 04:29:52 pm
I have found the mistake in wiring the test circuit, but this doesn't fix the problem. I'll get bac to the problem later. A blink sketch should help analyse the switching. Once I've got that sorted PWMing the LED should verify the switching.
45  Using Arduino / General Electronics / Re: mosfet switching on: January 18, 2012, 02:21:58 pm
Quote
1v across gate and drain

My mistake - 1v across gate to source.

Quote
Wired it up wrong or missidintified the pins or blown FET.

It worked first time at 6v, and thereafter not working.

Circuit diagram attached. Note - no pull down resistor shown on the diagram. Please ignore component values - no time to create parts for this.

Pages: 1 2 [3] 4 5 ... 10