Show Posts
Pages: [1] 2 3 ... 442
1  Using Arduino / Sensors / Re: Detecting a seed dropping through a plastic tube on: August 23, 2014, 06:27:44 am
If I were you, I would have tried this one with 5 mW laser & shielded LDR.


I respecfully disagree. A laser provides a narrow beam of light, but what is needed here is a wide beam to cover the entire width of the tube (which is why I suggested several LEDs). To use a laser, you would need to bounce the beam back and forth between two or more mirrors. And an LDR might be to slow to react to the speed of the blip in strength of the light when the seed passes.
2  Using Arduino / Project Guidance / Re: 4 stability, which LCD wiring? Parralell, SPI or? on: August 18, 2014, 05:31:35 pm
I've used 16x2 parallel-interface character displays for a couple of projects in the past, but these days I usually go for 128x64 graphic LCDs with SPI interface. I've not had problems with either, but I've read a few reports on these forums of people having what appears to be noise problems when using parallel-interface character LCDs.
3  Using Arduino / Project Guidance / Re: cheap PCB printing services on: August 18, 2014, 05:26:41 pm
I use itead for all my 2-sided PCBs and the quality has always been excellent. I usually select the low-cost airmail shipping, and then the boards get delivered to my UK address about 17 days after I place the order and supply the Gerber files.
4  Using Arduino / Sensors / Re: Detecting a seed dropping through a plastic tube on: August 18, 2014, 10:13:59 am
I'd be inclined to abandon the idea of trying to see them in the tube,    and instead consider counting the turns of the small wheel.

But that only tells you the rate at which you hope the seeds are being delivered, not the actual rate of delivery (or whether they are being delivered at all). It's better to measure outputs rather than inputs when you can. I think the optical approach should be entirely workable.
5  Using Arduino / Sensors / Re: Detecting a seed dropping through a plastic tube on: August 18, 2014, 07:26:03 am
Alternatively, put a single IR phototransistor with a beam half-angle of between 40 and 60 degrees a short distance from the wall of the tube (which I am assuming is glass), and put several IR photodiodes around the opposite side of the tube. No extra optics required, but you will need to surround the whole thing with opaque material to block out sunlight.
6  Using Arduino / Motors, Mechanics, and Power / Re: Brushless pumps; tacho(speed)-signal problems on: August 17, 2014, 03:23:34 pm
Check your BAT47 diode. If the pump produced an inductive spike, it may have exceeded the voltage rating of that diode and fused it.

I assume that the pump has only 3 wires (+ve supply, -ve supply and tacho), in which case you will have a problem with noise on the common ground wire. Instead of the BAT47, I suggest using an NPN transistor. Connect emitter to Arduino ground, collector to Arduino input pin (with pullup resistor enabled), 4K7 resistor between base and emitter, and 47K resistor between base and tacho output from the pump. That will give you much better noise immunity, and better protect the Arduino from any spikes on the tacho output.
7  Using Arduino / Sensors / Re: Detecting a seed dropping through a plastic tube on: August 17, 2014, 03:10:16 pm
Optical is the way to go IMO. You don't need the seed to block the beam, just to reduce its intensity enough to be detected. You could use an RC network to average the phototransistor output, and a comparator (e.g. the analog comparator in the Arduino) to detect significant deviations from the average.
8  Using Arduino / Sensors / Re: ALPS EC11 rotary encoders... detents? on: August 17, 2014, 03:05:24 pm
For the Alps encoders I have used, the datasheet shows that the detent position is exactly aligned with one of the transitions. This is the exact opposite of what I want- the detent position needs to be stable. The Bourns encoders have the detent position midway between two transitions, which is far more sensible. So i never use Alps encoders, I always use Bourns.
9  Using Arduino / Programming Questions / Re: calling pinMode in the constructor on: August 17, 2014, 02:59:04 pm
and in particular it should not be trying to initialize the LCD in the constructor, because the power may not yet have stabilised and the LCD may not be ready.

There is a 50ms delay hanging out in there and a comment that goes with it that claims that it is for just that reason. 

50ms is an arbitrary value. If the begin() call is removed from the constructor, then the user can choose how much delay (if any) to use before calling begin().
10  Using Arduino / Programming Questions / Re: calling pinMode in the constructor on: August 17, 2014, 11:21:31 am
The LCD library is badly written. It should not be calling pinMode in the constructor, and in particular it should not be trying to initialize the LCD in the constructor, because the power may not yet have stabilised and the LCD may not be ready. I use a modified version of the LCD library in which the constructor does not call the begin method (and I have made a few other changes too).
11  Using Arduino / General Electronics / Re: How to get an output voltage of 9V from arduino uno?name some ic's for it. on: August 17, 2014, 11:17:18 am
You haven't said why you need 9V or what the application is, so we don't know how much current you need at 9V and it's hard to answer your question. But you are probably better off powering the Arduino with 9V to begin with, and then using a few extra components to get the Arduino to switch the 9V to whatever needs it.
12  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 15, 2014, 05:47:30 am
so a beagle bone with 1GHz processor and having  32-bit timers won't help?what's the reason for that?

I may have been wrong. I see now that the processor used on the beaglebone has an ECAP unit. It's not completely clear to me what the maximum clock frequency of the ECAP unit is, but it may be high enough for your purposes. So if the beaglebone board brings out the ECAP pins from the chip to somewhere you can get at them, you may be in luck.
13  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 15, 2014, 05:20:09 am
Having a beaglebone won't help, the issue is that you need a 200MHz+ counter with an input capture facility. FPGA is probably the best solution, but I can't help you with that.
14  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 15, 2014, 05:01:36 am
PS - if what you are trying to do is to measure time of flight, then there are chips available to do this with resolution of a few 10s of picoseconds, such as the TDC-GP22 and MAX35101.
15  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 15, 2014, 04:53:11 am
The Duet master clock period is a little under 12ns, however the fastest clock that can be used for the timer/counters is half the master clock frequency.

To obtain a resolution of 5ns you will need to clock the counter at 200MHz or greater. I am not aware of any CMOS or TTL devices that can count this fast. So I think your only option may be to use emitter-coupled logic (ECL). I have only used ECL once, and that was many years ago. Looking at some datasheets, I think you could build a solution using about four 10E016 8-bit synchronous counters, some 10EL01 gates to link them together, some 10E131 D-flipflops to condition the input signal, 10E175 latches to latch the count, and some ECL to CMOS or TTL converters.

You might wish to google "Time to digital converter" for other possible solutions.
Pages: [1] 2 3 ... 442