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If you hate America and want to give your hard earned money to the evil Chinese empire, you can get super bright LEDs for about 10 cents each from this guy on Ebay. What makes this guy stand out is that he offers free shipping. He also gives free 470 ohm resistors which will work fine for 9-12V. I have no idea how this guy makes a profit. I've placed several orders with him and have no complaints. However, shipping does take a couple weeks. For small projects, I've been using prototype boards from this other guy on Ebay. They are pretty handy because each group of three holes is jumpered together. These are shipped from California, but don't let that fool you. When you buy from him, your money is going directly to Tiananmen Square to buy fuel for the Death Vans. Electronic Goldmine is a great place for real cheap variety packs of components to get started with. In the "GoldPaks" section, you can find assortments of various components for $2.50 each. If you look in the LED assortments, you can find a few variety packs from $2.50-$10 that break down to about 4 cents per LED. Pick up a couple of these and you can experiment to your heart's content without worrying about frying a few LEDs here and there. A computer power supply is a cheap alternative to a real bench supply. You've got your 12V (yellow), 5V (red), and 3.3V (orange). You can mix and match for other voltages as well. For example 12V hot lead and 5V on the ground side gives you a 7V power supply. A Google search on "ATX Bench power supply" will bring up several hits showing how to modify an ATX power supply to use as a bench supply. There are a few things to keep in mind when looking over these tutorials: 1. Some of them say you need to add a power resistor. I've only found one power supply (an older one) where this was necessary. Power supplies do require a load to operate correctly, but most of them have the power resistors built right in. On the 20 pin ATX connector, short the green wire to ground (black wire) then check to see if you are getting 12V between the yellow and black wires, and 5V between red and black. If those voltages are present, then you don't need to add a power resistor. 2. You can use the -12V line with the +12v or +5V lines to get +24 or +17 volts out of your supply, but the -12V line is not capable of handling very much current at all. For example, the one I am looking at is rated 5V=30A, 3.3V=20A, 12V=12A, and -12V at a paltry 0.8A. I'd just skip it be satisfied with +12V, +5V, and +3.3V. 3. You will short out your power supply at some point, so stick some fuses in there. Electronic Goldmine sells fuse holders and fuse assortments, so pick some of those up and toss them in there.
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Jan 9, 2008 07:13
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scholzie posted:Of course if you run it at 75mA you're looking for trouble. Kids, don't test your expensive super-bright LEDs by sticking the leads on a 9V, even for just a second. You're going to waste your money. On the other hand, you'll get to see what melting semiconductors look and smell like. I was using a 12V supply with a 1K variable resistor to give my nephew a practical demonstration of Ohms law and how it affects LED brightness. We had a cheap green LED hooked up and decided to see how much abuse it could take. I don't know what it was rated for, but at around 85mA it turned bright yellow and pushing it up to around 100mA made it turn a deep angry red color. I quickly backed down and it returned to green, but not quite as bright as before. After doing this a few times, it burnt out, but it was kind of an interesting experiment. Unfortunately, we weren't able to get any to explode at 12V. As a side note, the "superbright" LEDs (6K-15K mcd) I have are rated around 20ma with a max of 30mA. In testing, I didn't see much change in brightness between 20mA all the way up to 40mA and they were plenty bright running as low as 15mA. I don't see any point in pushing the limits just to get that extra little bit of brightness out of them, so I generally run them at, or slightly below, what they are rated for. My methods would probably make and EE sick, but I would rather be playing around with a breadboard then muck around with a bunch of math. When working with LEDs, I'll generally start with a resistor that I know is too high and work my way down until the LED is "bright enough" (usually 15-20mA). From there, I feel the resistor to see if it is running hot. If it is uncomfortable to the touch, then I'll either move up to a higher wattage resistor, halve the value and put 2 in series, or double the value and put 2 in parallel. I make that decision based on what's available in the parts bin.
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Jan 9, 2008 07:49
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scholzie posted:As for your resistor methods, I guess worse things have happened. You're wasting your time though because Ohm's law is just about the easiest thing to do in electronics. The reason I do it that way is because of the unknown LED values and lack of data sheets. Looking at this reference chart, it show a range of 1.5V to 3.8V at 20mA depending on what color LED you have. Also, the resistance of an LED changes based on how much current it is using, so you'd have to figure out that value as well if you planned on running them at something other than 20mA. I find it is just easier to plug the LEDs into the breadboard, hook up the multimeter, and try a few different resistor values. scholzie posted:Assuming your resistor is about 50-75Ω, and your current is about 25mA, P = I2R = 0.03-0.05W. Even that example above, 50mA and 2.9 volts is just 145mW. It's very possible I'm in the wrong here, but those numbers don't look right to me. 50mA would be 145mW for the LED at 2.9V, but if you're powering that LED with a 12V supply, then the resistor would be dropping the other 9.1V at 50mA and dissipating 455mW. Not that I can see any reason why you would want to power an LED at 50mA, but if you did and are using a 12V supply, a .25W resistor wouldn't cut it. You're right that at 12V and below in the 20-25mA range that a .25W resistor should be fine for whatever you are doing. When I mentioned using a higher wattage resistor or multiple lower wattage resistors, I was getting another project where I had to do that mixed up with some of the LED stuff I've worked on.
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Jan 9, 2008 12:44
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Here we are talking about using a 12V supply to light up LEDs (first mention of 12V).SkunkDuster posted:I was using a 12V supply Here is Scholzie referencing that post (no mention of 5V anywhere): scholzie posted:As for your resistor methods, I guess worse things have happened. You're wasting your time though because Ohm's law is just about the easiest thing to do in electronics. Also, you're dealing with voltages and currents that are so low you'll never need more than a 1/4 watt resistor. Assuming your resistor is about 50-75Ω, and your current is about 25mA, P = I2R = 0.03-0.05W. Even that example above, 50mA and 2.9 volts is just 145mW. 1/4W resistors are going to be ok for pretty much anything involving LEDs unless you get some of those crazy Luxeon LEDs with 1.5A max currents. Here is a 1/4W (250mW) resistor failing miserably in Scholzie's scenario (second mention of 12V): SkunkDuster posted:if you're powering that LED with a 12V supply, then the resistor would be dropping the other 9.1V at 50mA and dissipating 455mW. Here is Scholzie backpedaling. scholzie posted:The above example used a 5V source and a 2.1 V drop across the diode. Therefore, the drop across the resistor was 2.9V @ 50mA. And finally, we have Scholzie giving out some information that is flat out wrong: scholzie posted:Also, the spec sheet for that LED gives the Absolute Max. current as 70mA. You're not going to kill it with 5mA over spec as you alluded to. You'll just reduce its lifetime a little if you run it consistently (i.e. long periods of time) at that current. With your vast experience in semiconductors, didn't you look at your post and think "drat, 70mA is awfully high, really loving high, for a regular LED. Maybe I should take another look at that data sheet to see if maybe I missed the word "peak" in there"? Then you completely contradict yourself in the very next sentence and give out information that is absolutely correct. High five, buddy! scholzie posted:Of course if you run it at 75mA you're looking for trouble. And some more poo poo that is dead wrong: scholzie posted:you don't have to worry about the strange I-V characteristics of an active diode. Once the LED is active it's almost a perfect ohmic device with a fairly steady resistance I've plotted the "strange I-V" characteristics for a few of the LEDs I commonly use and I wouldn't call a 358% variation in internal resistance an "almost perfect ohmic device". The 14K mcd red LEDs I have drop 1.9V at 10mA giving them an internal resistance of 190 ohms. If you push them up to 40mA, the voltage drop increases to 2.13V with an internal resistance of 53 ohms. I had planned on plotting the curves for all of the various LEDs I have to use as reference sheets, but I stopped after plotting red, orange, and ultraviolet because I realized that... scholzie posted:You're wasting your time though because Ohm's law is just about the easiest thing to do in electronics. ...I was wasting my time plotting all these graphs when it was a hell of a lot quicker to just stick the LEDs on the breadboard with my multimeter hooked up in series to measure current, and then SkunkDuster posted:start with a resistor that I know is too high and work my way down until the LED is "bright enough" (usually 15-20mA) It's not that I don't know the formulas, I just don't think that working them out on paper is always the most efficient way to build a circuit to light up some LEDs. If you just want to make a few LEDs light up, it is a lot quicker to just go straight to the breadboard and measure the results firsthand. Your posts seem geared towards people who want to become electronic engineers and think about substrates and whatnot. Mine are geared towards the average goon who wants to add an LED to his PS3 controller to make the Playstation logo button light up without setting anything on fire. scholzie posted:Regardless, I see your point, but I think that's a bad way of going about design, even from a hobbyist standpoint. Sure, it works for one LED, but what if you have 10 of them, neither in parallel nor in series? 25? 50? I'd have to consult Schrödinger on that one. I know where you are coming from, and have read the warnings against using LEDs in parallel or series/parallel, and I'm in agreement with you that spec sheets and margins of error are for pussies. Still, resistors cost about 2 cents each, so why would you bother taking a chance on the remote possibility of a runaway current situation when you can just wire them in series and use a few extra resistors? If I was going to light up 50 LEDs, I would start by ignoring the number 50 and look at how many LEDs I could light up in series with my supply voltage. If I had a 12V supply, and I ballparked each LED to have a 3V drop at 25mA... scholzie posted:25mA @ 3V always works for generic LEDs ...then I would stick 4 of them in series with a small resistor to counter the dreaded runaway (better safe than sorry). If they lit up and looked good, and fell somewhre in the 15-30mA range, then great! If they were running a bit hot, then I'd increase the resistor value. If they didn't light up, I'd drop back to putting 3 in series and go from there. Your math and formulas are dead on correct, but some of the stuff you have posted in this thread ranges from unclear to completely wrong. This is a great thread and I agree that scholzie posted:this thread is all about getting started in electronics, I think people should get started doing it the right way so please take a couple minutes to look over your replies to make sure you are talking about the same thing the person you are replying to is (12V vs 5V) and your facts are correct (75mA PEAK voltage). I'm also looking forward to this: scholzie posted:Maybe someone (or I) should do a soldering tutorial. If there's interest maybe I can do it. scholzie posted:I sometimes gauge my productiveness by how many burns I got that day. With that aside, what the hell is the 5th band on this resistor for?  The orange-orange-orange-gold bands tell me that it is a 33K resistor with a 5% tolerance, and my meter is in complete agreement. So what is that yellow band at the end indicate?
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Jan 9, 2008 20:28
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Phlegmbot posted:If I were actually trying to learn electronics from this thread, I'd be so drat confused. Rightfully so. This thread is all over the place. In the OP, there is a link to the free online series, Lessons in Electronic Circuits. Those books start from the very beginning and explain things very well. There is even a lesson on power dissipation that intentionally has you burn up some resistors. I thought that was a pretty neat way of hands-on teaching. Considering that they are free, you can't really do any better. If you would like to print hard copies, be warned that the illustrations are in color and you'll need quite a bit of paper and some way to bind it. I assume you can buy pre-drilled 3-hole color paper, so some of that and some binders may be the way to go. Or maybe Kinko's can print and bind it. I don't know.
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Jan 21, 2008 19:04
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I'm looking to make a 1/10 scale record player for a diorama. The record player is going to sit on top of a 1/10 scale 3D printed console TV set. The plan is to stick the motor, speaker, and electronics inside the TV set and have the motor shaft come up through the top of the TV set through the bottom of the record player to make the record spin. I'm planning to power the lighting and everything else in the diorama from a 5V power supply. My question is - how can I get a micro DC motor to turn at 33RPM or close to it? Vibration motors for pagers are very tiny and would fit well, but the slowest I've seen is 3000RPM. Could I use PWM to lower the speed of one of those motors down to around 33RPM or is there a better solution?
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Nov 1, 2021 04:26
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BattleMaster posted:What about a small stepper motor? With a microstepping driver you can get smooth and accurate motion at low speeds. If I could get one small enough, that would be great. It has to be tiny, though, because it is going to be inside of a box that is about 1.5" tall. Accuracy doesn't really matter much as it is just for visual appeal. If it is anywhere between 25 and 40 rpm, I'm good with that. edit: I see on Amazon there are very small ones available. I've never used a stepper motor before, so I don't know how to control it. Off to Youtube for some tutorials. Thanks for pointing me in the right direction! Skunkduster fucked around with this message at 05:08 on Nov 1, 2021 |
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Nov 1, 2021 05:04
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babyeatingpsychopath posted:I've got some GM gauge cluster stepper motors that can be directly driven from microcontroller pins. They're geared so they already have really small steps so you can get very smooth motion at 30RPM. 30mm diameter, 24mm height to the end of the shaft, can shrink that down to 19mm if you don't mind a bit of surgery and some soldering. They're sold in 8-packs on amazon for like $20 or something. PM me and I'll drop one in an envelope for you. Thank you for the kind offer. Before I put you through any trouble, I'm going to need to learn more about stepper motors and design the TV set to see how much room I have inside. I'm assuming, at minimum, I'm going to need to put the stepper motor and some sort of Arduino inside the TV and possibly a driver board depending on the current draw of the motor. I might also have to stick an mp3 decoder board and a speaker in there, so space is going to get tight real quick. I have a long way to go in the design of this project. Right now, I'm just in the "gathering ideas" phase. Also, thank you for the description of the stepper fundamentals.
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Nov 1, 2021 13:55
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Ambrose Burnside posted:re: wanting a slow + consistent motor, a stepper is workable (especially if this is only going to be infrequently activated for display) but not ideal, it'll run hot as poo poo and generally waste a lot of energy holding things stepwise despite the lack of any loading requiring that energy expenditure. given your need for ~33RPM, look into synchronous motors, they're cheap, come in fairly small sizes, run off AC mains voltage, and are inherently suited to running accurately at a low RPM in the exact range you need. you won't even need a driver or any other parts, the platter can be directly driven from the motor shaft, if you don't care about vibrations like you do in a real working player anyways. they're motors that are inherently synchronous with the AC supply frequency of 50/60hz, which serves as an extremely accurate clock signal;they're what are normally used for real record players, iirc, alongside other applications like clocks, microwave turntables, sometimes washer+dryer timers, etc. just browse a couple distributors' catalogs and/or aliexpress to get the lay of the land and pick the smallest you can find that meets your voltage and RPM requirements That sounds good, but I'll be running this off either batteries (18650 because I have a hundred of them) or a 5-9V power supply as the only other electronics in this diorama will be some LEDs. The accuracy isn't very critical. It is just a scale replica of a record player so if runs at 30-35 or even 25-40rpm, I don't think anybody would notice.
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Nov 4, 2021 00:25
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poll plane variant posted:I figure this is as good a place as any to ask: I need some bright overhead lighting for a workbench, I don't want to hack into the ceiling too much because I'm probably moving next year, but my wife says that anything linear (fluorescents, LEDs, anything in a line or strip) looks "too cheap". I was going to do the conventional "LED strip/fluorescent on poles coming off the back of the bench" like everyone does, but that's out now and I didn't know if any of you had seen super bright non-cheap-looking lights Just buy a new refrigerator and mount that over your workbench. I've heard the lights in those are bright as hell.
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Nov 5, 2021 19:02
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His Divine Shadow posted:Nobody here sends on MW anymore so that dates it a bit. But all I found inside was an old ferrite wound antenna, I didn't know those could get FM reception too, but it's all I found. I've never seen a radio where the AM band was labeled MW. Is this a European thing?
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Nov 8, 2021 14:14
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Reminds me of this story about the history of glowing clock hands and radium poisoning in the Waterbury's Radium Girls. https://connecticuthistory.org/waterburys-radium-girls/
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Nov 10, 2021 00:39
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I'm looking to get a combination soldering iron / hot air rework station. =At work, between 3 people, we have been using varations of this pile of poo poo. I also bought one for home use that died recently. I think we have gone through 6-7 in as many years including one where the heating coil in the rework gun burnt up on the second day of use. We replaced them with two even cheaper models and both of those were faulty right out of the box. We'll keep replacing the ones at work with lovely ones as they crap out, so that isn't a problem. I'm looking to get one for home use to replace the my personal one that crapped out. Cashwise, I'm not in the Weller range, so I am looking at something in the $300-$500 range. I'd almost prefer one that doesn't have a built in power supply as that is a feature that costs money that I don't need. Just a reliable soldering iron and hot air rework tool is all I need. No frills. Any recommendations? edit: to clairfy, it will obviously need a built in power supply to power the unit. I meant one of the units that functions as an external variable power supply. Skunkduster fucked around with this message at 03:27 on Dec 22, 2021 |
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Dec 22, 2021 03:03
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ANIME AKBAR posted:e: looks like weller was acquired and discontinued the WES51 and WESD51, lol owned What is the context of this? I have a Weller iron that is similar to the WES51, but without the heat control. The heat settings are "off" and "hot enough to weld steel". I'm going to look at modifying it to add heat control and took your advice to get a dedicated hot air station: I do a lot of soldering at work, but just occasional hobby use at home mostly with through hole stuff. I don't need anything fancy, I just want something reliable that isn't going to crap out after 20 hours of use. I probably should have mentioned that I very rarely do any SMD work at home. I mainly use the hot air for removing components and heat shrink.
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Dec 24, 2021 06:22
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SkunkDuster posted:What is the context of this? I have a Weller iron that is similar to the WES51, but without the heat control. The heat settings are "off" and "hot enough to weld steel". I'm going to look at modifying it to add heat control and took your advice to get a dedicated hot air station: Upon closer inspection, it is a Weller WTCPT base with a TC201T iron that appears to have a stuck thermostat. I don't think it is repairable and a replacement iron is $100 on amazon. I'm not sure if I want to spend $100 to have a working soldering iron with no heat control. Then again, I'd rather spend $100 to have an iron that will last for the rest of my life, than spend $250 for one with a heat control that will crap out in a few years. Need to think about this one. Skunkduster fucked around with this message at 15:07 on Dec 28, 2021 |
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Dec 28, 2021 15:03
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Foxfire_ posted:A fx-888d is about $100 and is a perfectly cromulant entry level iron that has accurate heat control and won't fall apart I will swear to my grave that the $7 Hakko CHP-170 wire cutters are every bit as good as any $50-60 wire cutters on the market, so this seems like the best option. Thanks! ante posted:I plug it into a powerbar that also powers the bench lighting. Pretty good "possibly on" indicator imo I like that idea, but I 2-3 battery chargers connected to the same power strip as the soldering iron.
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Dec 29, 2021 04:13
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That turned out very nice and clean. My first two thoughts were to ask how you did the decals and what does the inside look like, so I'm glad you answered those in your post.
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Jan 9, 2022 21:35
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Rescue Toaster posted:Does anyone have a helping hands setup they're happy with? 9 times out of 10 when I'm doing a connector I can NEVER get things positioned in a way I'm happy with, even with multiple different helping hands tools/clips/whatnot I have around. I bought one years ago and ran into the same problems you did and never use it anymore. I solder up a lot of small connectors for work and this is my go to vise for holding the connectors. We use three of them at work and I have one at home. The vacuum bases aren't very good, but it is solid enough that you don't really need it. https://www.amazon.com/Bessey-BVVB-Vacuum-Base-Vise/dp/B0057PUR88/
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Jun 27, 2023 14:26
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I like the Bessey vise because I can flip it around sideways and steady my hand by resting my palm on the ball because I am old and have shaky hands. My pinkie also helps keep me steady and is not as close as it looks to the hot barrel in the picture.
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Jun 27, 2023 18:17
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Cojawfee posted:You'd get better control if you choked up on the iron a bit more. Like this?
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Jun 27, 2023 18:29
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kid sinister posted:Oh the things you learn when repairing old radios. When selenium rectifiers go bad, they smell. I haven't smelled a burnt selenium rectifier, but I used to routinely replace voltage converters that burned up and spilled brown goop all over the board. You could tell one went bad by just sniffing the equipment. My coworkers thought it smelled awful, but it brought back memories from the late 70s for me when lightning struck our aerial TV antenna and cooked the box next to the TV that positioned the antenna. Some smells you just never forget.
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Jul 8, 2023 02:04
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Cojawfee posted:Uh, ok This post is a beautiful post. 
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Jul 31, 2023 18:07
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I would blow Dane Cook posted:bit of a long shot but does anyone here have any experience with the altera usb blaster (the FPGA programmer) or more specifically the cheap clones from ebay/aliexpress? I use an Altera USB blaster occasionally at work, but have never used the ebay clones. What's your question?
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Aug 9, 2023 18:07
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I would blow Dane Cook posted:I was able to install the driver and get it recognized by windows easily enough. But I have not been able to get it to show up in the quartus prime programmer software. Tried different computers. Even tried linux. I am now trying to get another one to try. I'm not at work right now, so I can't check the configuration. Also, I'm not sure what Quartus we use, but I don't think it is Prime. With whatever version of Quartus we use, it doesn't have the Altera as an option - just select USB. I think that even though we are connecting through JTAG, we select Active Serial (instead of JTAG) and it works. I don't know or understand the communications protocol at all, but I hope that maybe gives you a couple things to try.
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Aug 10, 2023 04:21
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