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You seem quite preoccupied with Mr. Randi

So, he has no monopoly on negative feedback. Can imagine trouble he caused for well meaning people just doing their job in more clever way vs average Joe who is helpless w/o truckload of gear.



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Repair / Re: Fluke 8800A
« Last post by neo on Today at 04:32:07 AM »
OK i'm at a loss here, there is a plain white wire, the point i'm almost certain it belongs to is marked as TP14.
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Beginners / Re: Hiss with AC-DC buck supply: how shielding ?
« Last post by janoc on Today at 04:21:19 AM »
yes, mammut is properly a terminal strip.
From what you write, if I understand correctly, I deduce that I can use two terminal strips, one for the positive reference and the other for the negative reference. But if the chassis on which the pedals are fixed is made of aluminum, like this https://cdn.marcmart.com/ebay/EC916/3.jpg, could not i drill a hole and make all the ground converge here ? Or do you say that there is some impropriety and better to use two terminal strips, one for the positive reference and one for the negative one ?

You don't have to drill a hole into chassis. It would be better if the chassis was grounded but it doesn't matter all that much in this case. Just make sure the chassis is insulated from the pedals in such case in order to not create another ground path, circumventing your star ground.

Of course, if the pedals are screwed down onto the chassis it would be probably better to install the ground there to avoid problems.
You can still use two terminal strips, one affixed directly to the chassis for the ground and one for the 9V.

45C is okay, but the rest about your supply still applies. That's not a supply that will withstand the rigors of portable use.

Why do you say this ? what problems could I go to?

See my comments about the lack of any mechanical support for the components - they are held in place just by soldering. If you drop the supply or toss it in you baggage, the solder joints and the tracks will be stressed - the component leads and the large size work like a lever. After a while they will crack and the components will not have good contact anymore. E.g. if the ground pin of the voltage regulators gets loose you will have a full input voltage at the output - likely quite a bit more than the 9V the gear is meant to work with, frying it. I have seen components even detaching from the board completely and causing a short circuit - quite a problem in a box where you have mains voltage.

Then there is the issue of the mains wiring (lack of fuse), the possibility of water/liquid ingress due to the holes you have made, etc.

Today the postman gave me the sheets of mumetal and placing them under the wah wah the hum of 50 Hz or 100 Hz disappears. I remember that the hum is generated when I use the power supply with the transformer putting it under the pedalboard together with the pedals. Now I have to try the power supply of Truetone with the star connection of the grounds.

Yes, don't leave it like that, happy that the transformer hum is gone. The current wiring will certainly cause you problems in the future.
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If you need two of them and connect both to the same 12V supply then you must be aware that these power supplies does current sensing on the negative outputs. This means that if you connect both power supplies to a common 0V (e.g. for +5V and +12V) then the common ground on the input (the boat) and common output (the device under test) will short out the current detection of the RD Tech units. These units really needs separate power sources...

Ah. That's a very good point, thank you! So the outups are not "floating" or "isolated" then? Hmm. I guess that means connecting two of them in series to get a symmetric supply (e.g. for audio amplifiers) is also out of the question :( What to do? Use a regular 240V PSU via an inverter?
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Beginners / Re: Arduino vs. "Bare Metal" programming
« Last post by retrolefty on Today at 04:20:28 AM »
It's not a huge hassle to program via the ISP. It needs some minor figuring out, but then it's fairly straightforward. I think I actually prefer it, because it makes the board super simple.

It requires an ISP programmer of course, which tend to be very cheap these days.
You could always shove done resistors in your  parallel port and program using it

About the main topic, you can usually, pretty easily adapt/reverse engineer the libraries to work with atmel studio.I did actually successfully do it for mlx90614 Library

 Easiest ISP programer for working inside the Arduino IDE is simply another arduino AVR board (such as a $3 arduino nano clone board and a 6 pin ribbon connector) loaded with the supplied example arduinoISP sketch. Works fine and there is no simpler ISP programmer solution.
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Repair / Re: Help me diagnose a scope problem? (Hitachi V1100A)
« Last post by zenrael on Today at 04:19:55 AM »
Apologies for the late update on this guys, bit of a busy week...

Okay so i took the casing off and it turns out that the boards are rather tightly packed. I took whatever pics I could with the caps you mentioned, but i imagine they're not very useful.

None of the caps looked 'bad', per se - there are some coloured dots on the caps for the CH1 preamp section that may have been added by whoever last calibrated it? Maybe they indicate caps that need replacing but the job was never done? There are no such coloured dots on the caps surrounding the CH2 preamp section.

They *look* fine, but i don't think i'd be able to check further without pulling everything out of the chassis. I may try this in the new year but for now I guess i'll just put up with the working CH2 and the semi-working CH1.

Many thanks for the input guys, if i do work on it any further i'll update again.

John
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A funny thought occurred to me, i have four 3.5 digit, three 4.5 digit and two 5.5 digit multimeters.

It seems as if my test equipment is ganging together to tell me i need 6.5 next...  :-DD

OK, sounds like a mathematically well-defined buying list.  ;)
So you want to increase your stock by three 3.5 digit, three 4.5 digit, three 5.5 digit, three 6.5 digit, two 7.5 digit multimeters for adding a 8.5 digit multimeter finally..   >:D    :popcorn:

I like your thinking, though that would have me winding up with only 24 meters.

Yeah.  In that pile.  Then you start another.   >:D

-Pat
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Microcontrollers & FPGAs / Re: Basic scheduling question
« Last post by jnz on Today at 04:14:48 AM »
Ok, most of that makes a lot of sense. I guess I had always called C a "state machine" as well, but knew it wasn't a "formal" statemachine so I didn't want to explain it to someone else with me just guessing.

I'm on top of most of this, just self-taught so never got the terminology. I've been using informal statemachines, and I think it's starting to make sense to go to a cooperative scheduler as I've already learned with RTOS that my projects are really too small to need it - and that RTOS really works best when you treat each thread like a separate statemachine and not a collection of each thread for each purpose.



Quick question about Coop schedulers...

The simplest one I've seen doesn't interrupt context on blocking. It's just a null pointer directed to your functions and calls them when they need to be called. I could "improve" upon this by adding the amount of time I can sleep until the next task, and for debugging I could save some data of what just ran and what will run next, easy stuff.... But saving context... How!? In your example if I wrote some blocking scheduler delay for 10ms and the system decides another thread should run - does the context switch back after my delay or does it wait until the more recently run code has finished?

Because in the former that's a lot of context switching and no guarantee of anything predeterministic, and the latter means my blocking scheduler delay could run for longer than I had intended. Both seem like they have issues.



Does anyone have an example of a small scheduler that uses context switching? I know Nordic has something like that on their BLE ARM chips, but also iirc they have a couple hardware or softdevice hooks to make that work.
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Beginners / Re: Guitar preamp op amp tl072 input noise
« Last post by Audioguru on Today at 04:13:15 AM »
The neck and bridge of a guitar are some wavelengths of sounds apart so their phases are very different at different frequencies. I doubt you can hear if one signal has its phase reversed and if both signals have their phases reversed then they will have the same phase.
Instead of amplifying each pickup separately, why not use a single amplifier with a simple balance control.

A magnetic guitar pickup produces a very high output level. Then an opamp or two Jfets are not needed. The preamp input impedance must be high to allow the pickup to resonate and produce a level boost at about 5kHz so ordinary low input impedance transistors cannot be used. Use a single Jfet like this attachment:
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Manufacturing & Assembly / Re: Professional assembly mishaps
« Last post by asmi on Today at 04:10:22 AM »
My own oopsie that happened this weekend  ::)
Decided not to fix as it's a 0201 cap which is too close to the DDR3L IC so that I couldn't get in there with an iron without risking damaging the IC. The module works at full speed just fine even without one cap :phew:
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