EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: localbroadcast on October 19, 2016, 07:41:03 am
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Hello. I ordered a DDS signal generator off of ebay a while back, and i fried the thing by doing something stupid with it.. i forget what it was... but i think i put supply voltage into the output or something dumb like that.. either way, the thing doesn't work anymore, (screen works, but there's no output where there should be output). There is an 8 pin DIP that is replaceable, so I am hoping this is the issue... unfrotunately I can't make out what the IC identification is.. or if I can make it out correctly, its not coming up on ebay or google with any results that make any sense.. Does anyone know what is a replacement IC that works in this thing, with the same pinout?? hopefully someone out there has had this same issue.. Thanks.
picture of the thing attached, and below is the ebay ad's description:
DDS Function Signal Generator Module Sine Square Sawtooth Triangle Wave
Features:
• Operating voltage: DC7-9V
• DDS frequency range: 1HZ-65534Hz.
• High-speed frequency (HS) output up to 8MHz;
• DDS signal amplitude of the offset amount can be adjusted separately by two potentiometers;
• DDS signals: sine wave, square wave, sawtooth, reverse sawtooth, triangle wave, the ECG wave and noise wave.
• 1602 LCD menu;
• Intuitive keyboard.
• Section into the value: 1,10,100,1000,10000 Hz;
• The power automatically restore the last used configuration.
• Offset: 0.5pp-5Vpp
• Amplitude amount: 0.5Vpp-14Vpp
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Its likely to be an 8 pin micro, I would imagine atmel or pic,
Use your camera at about a 40 degree angle with the flash on, should make it much clearer what the markings are
and if there is a brand marking it might make things much clearer,
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jeez i was hoping i wouldn't have to dig the thing out of the pile of broken electronics in the back of my closet... but i did just for you... k the thing is stamped with the following:
first line: 7650S < ------ the last 'S' might be a five and the zero could be the letter 'o' lol
2nd line: CPA , <-------- this is possibly part of the logo, as there is a stylized and underlined letter 'i' right above where it says cpa. on closer inspection, i think the stylized 'i' is a scratch in the plastic....
3RD LINE:240BDA <------- Again, the zero might be a letter 'O'
It seems that now i have no issue finding this datasheet.. and it seems that this is an opamp by intersil..
here's the datasheet.
http://www.mouser.com/ds/2/465/icl7650s-553829.pdf (http://www.mouser.com/ds/2/465/icl7650s-553829.pdf)
does anyone know if any of the common opamp packages have similar pinouts?? i have a wide selection of opamps in my collection.. lm324,lm358 etc.. and the only places i can find to purchase the intersil version is selling them at about 7$. I can get a new complete DDS function generator from ebay for like twice that price, so I don't see any reason to pay that much if i might already have another opamp in my collection that will do the job. also, i dont even know if the opamp is the issue, althought it probably is...
anyone wanna take a look at that datasheet and see if htey recognize that pinout??
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ICL7650S Super Chopper-Stabilized Amplifier.
I wonder what is it function in a cheap function generator. I guess it is an overkill for the offset control.
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That icl7650 does seem really out of place. To much precision for a non precise circuit, plus it needs 2 external timing capacitors.
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Probably a marketing-descision - "Super high prescision offset for perfect Audio-Measurements!" :D
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Could be, pdip-8, charge pump
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i originally thought it was an icl7660, and ordered a handful of those to try out. it did not work. ICL7650S is the part for sure.
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You can get a replacement, e.g ICL7650 (should be no need for the S version) and also alternative max7650 or LTC1050 which are essentially the same.
Depending on the supply voltage a normal OP could work as well. At 5 V supply I my guess would be an MCP6001.
It would be a rather strange choise to use this relatively expensive OP. So it could be even a different chip, just with fake marking. Can you show a picture of the board, including the area where the chip is ?
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it seems to have a very similar pinout to the common ne5534 opamp... which i have many of... dare me to power this guy up and see what transpires>??? its been a while since i played with this thing, and i may have completely garbaged the thing the last time i mucked about with it out of frustration.... lol... well... dare me or what??
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Go for it. it will either work, or not. You might have to cut some of the opamps not beeded pins, or leave them. I won't compare the chips
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OOOOK\!!11 tHINK I FINALLY GOT THIS ONE SOLVED!! (BUT NOT WORKING JUST YET) :horse:
OK HERE'S HOW IT GOES...
This function generator has two main modes... DDS generator (for sawtooth, sine, etc. at relatively low frequencies, i think maxing out around 30khz or something.. maybe a little lower? i know it gets about 15khz for sure.) the second mode is labelled HS, for high speed i believe, and this one can produce 1MHZ, 2mhz, 4, and 8mhz signals. So here's where I believe I've figged it all out.
okay, so the replacable chip that seems to be overkill for a DDS generator ACTUALLY IS overkill for the DDS because its the chip for the HS output! I realize now that there is a surface mount chip that is not made easily replaceable also on the board, and it is the very same and predictable, N5532 opamp! neat stuff, huh?? So.. whenever i feel like getting around to it, i can swap out that surface mount with one that's human sized, and see if i get any signals poppin on the dance floor that way!
This thing is based off an atmel chip... so... it's really gonna end up coming down to this...
How's this thing actually operating?? I mean... I've got plenty of arduinos kicking around.. and plenty of n5532 as well as a ton of other opamps... it would make more sense just to make my own version of this thing instead of fixing this broke joke.
I've been trying to find a good frequency generating library for the arduino, but none of them really work as well as I'd hoped.. and the real solution has been pointing to using external hardware with more accurate timing.. such as what we have with this little beautifully designed DDS function genny and her opamps!
So now the big question... how would you guys suggest I go about making the arduino oscillate this opamp n5532 at the frequency I deem it need be ticklin electrons at??
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"i think maxing out around 30khz or something.. maybe a little lower? i know it gets about 15khz for sure.)"
"How's this thing actually operating?? I mean... I've got plenty of arduinos kicking around"
Sounds like it could be PWM to me, especially if the 15 - 30 khz waveforms are a bit rough.
DDS doesn't seem to mean much these days.
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There are quite a few plan in the web, that show a simple DDS generator build with an Atmel AVR µC and an DAC. The µC is capable to output 8 Bit data up to about 2 MHz (with 20 MHz clock). So in principle one could get a sine signal up to about 500 kHz (with suitable filter). So the 0-65 kHz range is still relatively moderate to achieve and still leave quite some time for handling the LCD without glitches.
The NE5532 is a reasonable output amplifier for this low cost range.
An ICL7650 is really odd, as it is a rather expensive part. So I still suspect it was the wrong chip.
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The 7650 is definitely the chip that was originally on the board in the 8 pin dip socket. it handled the output range when you set the thing to the high freq. setting. The n5532 chip is also on the board but handles the lower frequency range, which is more specifically:
DDS frequency range: 1Hz-65534Hz (N5532 opamp)
high-speed frequency (HS) output up to 8MHz. (ICL7650 opamp)
So there we have it then... but my question is still this... if i took my arduino, and I took a n5532, what would be the best way to make it into a functional sinewave generator that could have the frequency adjusted by a potentiometer?? thats what i want. doesn't need the led output or anything... just a sine output from 0hz - 65000Hz by way of a trim pot.
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If it's any use.
It makes sense for it to be a 7660 and not a 7650.
This thread shows a picture of a board with same date and version number as the one 2 posts above.
http://vintage-radio.net/forum/showthread.php?t=110897 (http://vintage-radio.net/forum/showthread.php?t=110897)
This version gets the 8Mhz directly from the avr.
http://www.scienceprog.com/avr-dds-signal-generator-v20/ (http://www.scienceprog.com/avr-dds-signal-generator-v20/)
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Using a pot to control an DDS type generator is a little odd. It could be still done using the µC internal ADC. The more logical way would be using an incremental encoder or keys and a LCD to show the actual frequency. Depending on the program there will be glitches when changing the frequency.
For the DDS you also still need an DAC: either R2R (with usually not so good accuracy) or a 8 Bit DAC chip. Doing DDS in software usually needs a program in ASM, as the run time sets the speed. The pure DDS code is still relatively simple, but it gets more involved if you want the interleave it with handling the LCD and keys without glitches. So this is more like an advanced ASM project.
The other option would be a an DDS module (AD9850 based) controlled by the Arduino. Here the main part to build is the output amplifier and amplitude adjustment.
For analog control the XR2206 (Chinese clone ?) base analog generator might be the more suitable solution. You might still want to add an output amplifier.
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(Also, why do you keep writing N5532 instead of NE5532? It may not seem like a big difference to you, but N5532 doesn't mean anything.)
Because it was obviously a simple oversite? Everyone knows what chip I'm talking about regardless, and the only people who would be dicks about it are those who also think their shit don't stink, and thus refuse to flush the toilet on account of trying to honorably save water... when in reality, their shit stanky probably double hard on account all them beef burrito wrappers beside their laptop, and also their roomates been double flushin behind em cuz of what a dick the dude is!! So bro be wastin water, pissin off his roomies, and just be walkin around like he all king buffy! see where im goin with this?? im sure this post is doubly harder than understanding wtf n5555dizzle2 means.. ya dig? thanks for yur interest tho... and also, because the chip reads N5532.... :) im sure other manufacturers may have it differently.