DSO-138 Oscilloscope build walk-through - avoiding the pitfalls

this is a fairly detailed walkthrough aimed at the novice now there are close-up photos and videos so use the pause button if needed there are also tips to help ensure it works first time so here's what you start with just a bag of bits and here's what you'll end up with a nice little tool for exploring low-frequency waveforms or DC levels and it will even run off a battery you can also buy a see-through acrylic case to protect the units and this has cutouts and extensions to operate the controls so it can look like this but more of this later now ignore those who say this is junk or just a toy as I think they're confusing things which don't meet their particular requirements which isn't the same so as long as it meets your requirements then it's a perfectly usable tool even a hundred Meg scope is of limited use to a microwave engineer besides that there's a lot of work gone into this so dismissing it as junk isn't very complimentary to the hardware and software design engineers some soldering skills are required but it's a fun kit to build tricky in places but that's all part of it and you can even try linking it to your PC and flash the latest firmware all of which is good learning experience for the growing number of gadgets nowadays which use these powerful single chip microcontrollers now the first tip may be obvious but read the instructions otherwise known as RTFM and the second tip is don't rush if you solder things in the wrong place it's unlikely to work and may damage the item or cause knock-on damage to other components and even if you do notice before switch on unsoldering andrey soldiering could cause more damage to the component or the board so get it right first time here's the set of tools they advise but treat this as a minimum I would certainly recommend an anti-static mat and wrist strap to avoid any danger of destroying the delicate chips or just as bad subtly damaging them so they break down after a short time just like insurance you may get away without it but if it doesn't work when you switch on there always that element of doubt now if you don't have side cutters for snipping off component legs then nail clippers would do it a push but get permission if they're your partner's okay RTFM again always meter resistor values here's a multimeter basic ones measure resistors but the more you can check the better this one can also check capacitors and transistors so why do you need to check resistors aren't they all color-coded well yes and no back in Stone Age resistors had three colors and a tolerance band in gold or silver now they have five bands and can appear ambiguous as they can be read either way around and I can hardly see them so other useful tools are a magnifying glass and if you're more serious headband magnifier so what's in the bag as the main printed circuit board or PCB now this kit is the 1/3 803 version which has pre soldered chips and pre-sorted surface mount resistors and the o4 version lets you solder the micro miniature resistors yourself which is tricky but doable so decide which sort of challenge you want before ordering all the info is on the jye techcom website and the display board is separate and plugs into the main board when everything is soldered up the LCD panel is stuck to its board with double sided tape but mine was misaligned so the seller offered to send a replacement now it is possible to prise away the panel from the board using a hairdryer to soften the sticky tape but you could cook the LCD or fracture it so I only attempted this as I knew a spare was on its way and luckily got away with it here the resistors 23 in all and again it says to meter the values before soldering so 3 100 KS 3 1 KS 3 120 s check and so on the instructions include tick boxes so you can keep track of progress now the chokes are also color coded I couldn't check inductance so decided a resistance check would be good enough and mine were 3 point 4 ohms so at least they weren't open circuit or a short circuit the diodes are marked with their type number and I use the diode test mode on the meter to check the forwards voltage drop and reverse resistance this is the 4 double O 4 Ford's voltage is 0.8 volts and reverse and this is the v 8 1 9 it's a Schottky diode so has a smaller forward drop of 0.2 3/8 in my case reverse these look fine all I can do with the crystal is confirm the frequency marking check the switches should be open circuit until pressed as ceramic capacitors the 104 code means 10 followed by four zeros in Pico farad's that's 100,000 which is not 0.1 microfarads and there are 11 of these and all of mine were below spec ranging from 0.065 to 0.074 so this could either be a faulty batch or my meter is miss reading I've never checked the capacitance calibration so decided to risk it and proceed now the others seemed much better one two one is 12 followed by one zero that's 120 Pico farad's this was spot-on and the other one was one one six so good enough the 22 Pico farad's a 330 a three and the one now the LED can be tested by using the meter in resistance mode where it acts as a low voltage low current power supply the LED will light up if the longer lead is connected to a positive voltage now on my meter this is the red lead pretty obvious you'd think but if you have an old analog moving coil meter like this it could very well be the black lead and make a note of this as you'll need it later for the electrolytic capacitors moving on to the transistors two types I could have chatting with the multimeter but forgot probably a senior moment regulators also two types and though they only differ by a single digit one provides +5 volts the other minus 5 so they couldn't be more different so don't mix them up and use that magnifying glass the capacitor trimmers and these are outside my meters range so I just checked for short circuits the electrolytic and mine were all marked to 20 micro farad's but I decided that bigger values would be okay and these are also outside the capacitance range on the meter but you can still check them by using the meter as the simple power supply as before use the resistance mode to charge them up then voltage mode to see if they're charged now you should only charge them the correct way round so before you try this make sure you know which meter lead is positive when it's in resistance mode and as mentioned older moving coil meters tend to positive on the black lead when in resistance mode it's not obvious but that's just how they worked now if you haven't got another meter to check which lead is positive catch-22 go back to the led step to see which way around causes it to light up so check the residual voltage short the pins reverse the leads if necessary then switch to resistance mode to charge up switch to voltage mode to measure and short the pins again to leave it discharged now you should probably use the resistor to discharge the capacitor more slowly but I don't think this one-off test with a low voltage will hurt a pin headers a three pin and four pin that may be obvious but it's the smaller pins which is soldered to the board and if you solder the four pin first there's no chance of mixing them up it's a swine to put right if you get it wrong okay next batch hardware and power inductor now as with the chokes you can check the resistance on the power inductor a mine is 1.6 ohms you can check continuity for the power conductor and the same for the slide switches now each row of five pins the check separately and the central pin connect to the other three pins corresponding to the three positions of the slider we've got right middle and left and repeat for the other row of five left middle right the BNC connector I just checked for continuity and shorts right ready for soldering but we'll just check the existing components first all joints should be bright and shiny this is the ARM Cortex processor which looks fine by the way this is a great little gizmo for a budding enthusiast so I can recommend getting hold of an evaluation board which are cheaper chips on well-known auction sites and their use is just limited by your imagination now other controllers are available anyway the quad op-amp looks ok and the 3.3 volt regulator well are mine the sole ring looked a bit dull so I resold it the pins okay now we can start I'm sure everyone would have their own tips and preference for doing this but these are mine I'm used to scraping component leads to remove tarnish which would impede the flow of solder and you can see why they tarnish from my antique resistor collection now there should be no need to do this with new components but old habits die hard when you're bending the leads use tweezers or pliers between the body and the bend to avoid stressing the joint and to bend the lead so they always line up with the PCB holes you can get a bending template or just use the tweezers taper or pliers jaws as a simple guide and if you orientate the components the same way round it's easier to read and check their values later you can hold the components in place before soldiering by bending the lead slightly outwards now you can place and solder one component at a time but I find it's easier to do a batch and as there's only 23 resistors in this case placing them all first gives you yet another check that they're in the right positions before soldering and finally just be aware of the damage caused by overheating so either pause between the two legs of one component or solder one leg in a group of components first and come back to do the other side so each one is at time to cool down blowing also helps use an adequate iron and a damp sponge for keeping the tip clean the instructions advise 20 watts and if the iron is underpowered you'll end up holding it on the joints longer than necessary and run the risk of damaging something now I have a 15 watt iron with a nice small bit but this wouldn't be up to the job so had to resort to the 25 watt iron with a much larger bit now this bit is just about okay for most of the pins in this project but I'd recommend a smaller one the only pins which is too close to risk are the USB connector and slide switches so I use the 15 watt iron for these okay now the solder ring I'm sure you can do a much neater job with the proper bit and without the cameras running but you get the idea apply heat a fraction before the solder and don't hang around snip off the legs and inspect and scrape off any solder splashes I keep a few off cuts for making test connections later solder the switches now as with several of the multi leg components solder just one of the pins first then press the component gently against the board while dabbing the iron on the joint they should then reseat itself flush with the board so you can then solder the other pins the USB socket is not currently used in this kit all the reflashing is done with the 3-pin header I don't know if it will ever be used but might as well fit it just in case this shows how much closer the pins are and why a fine soldering tip is needed right here's a spin around the board showing a few more components fitted with these switches or flush-mounted I left the power inductor till last as it's a larger version than when the board was designed I wouldn't normally matter as you can bend the leads so that it fits adjacent to the large capacitor but you may need to think ahead if you're planning on fitting it into the acrylic case the case uses a sandwich of plates as spacers to hold the display and main board this means the plate below the display has pre shaped holes so it clears the tallest components on the main board now if you mount the inductor in its intended position its diameter is slightly larger than the hole which isn't a big deal as you can enlarge the hole with a file but the real problem is that it's so tall it sticks through the lower plate into the next one and that one doesn't have any holes so the options are to either fit the inductor horizontally or in a different position there's a gap between the board and the back of the case so there are a few possible locations or you can make a hole in the second spacer plate but then you run the risk of cracking it or you can do what I did and leave out the spacer plate altogether and just use spacers or nuts on the fixing bolts so here's the inductor fitted vertically these are the connectors for mounting the display to the main board there are some alignment issues here especially if you want to use the acrylic case so you could leave this step till you're ready to assemble the display board either way make sure you use the females on the mainboard and the males on the display board if you mix them up it will still connect and work but you won't be able to swap boards if ever you need a replacement or get another kit and also make sure the two pin headers are aligned with the board edge otherwise they won't fit those on the display board right the BNC socket this needs a lot of heat to solder so to minimize the risk of the central pin moving as the plastic surround softens connect a plug before you sold it and the spot of glue between the socket and the board will reduce the strain on the solder joints when in use and you can also glue the DC power connector for extra support I hope you save those cut offs you can also make some pins for the ground connection nearly ready for power one vital step short-out jp3 right one final inspection for any solder splashes or bridge pins and time spent here will save endless hassle later if it doesn't work right now for a power supply a three things to check the voltage current and polarity of the plug the central pin should be positive and a spec says 8 volts to 12 volts will do but do not succeed 12 volts 9 volt battery such as a PP 3 will be fine although make sure it's new or in good condition you could use a 9 volt up converter running from a 5 volt USB supply now I checked several old mains adapters or wall watts but the off load voltages were over 12 volts so I didn't want the risk using these I did find one which measured just over 9 volts off load and with a current rating of half an amp which is more than enough the spec says the scope draws at least 200 milliamps that's not 0.2 amps at 9 volts so whatever supply you choose you should confirm it and deliver this otherwise the voltage may drop too low and you'll end up chasing non-existent faults now a bit of Ohm's law shows that a resistance of 45 ohms will draw 200 milliamps that's nine divided by not 0.2 so if you've got some resistors handy you can use your meter to check they only connect the resistor across the supply just long enough to take a reading it will be dissipating 1.8 watts that's I squared R which is 0.2 times 0.2 times 45 so you'll fry it if it's a low power resistor and you leave it more than a split second I was curious to see if my 0.5 amp supply was rated ok so use that large 18 ohm resistor and this draws the full 0.5 amps and I found the voltage drop from nine point three nine to eight point nine six so this is perfect for the scope albeit a bit overkill alright finally time for the smoke test connect the supply and cross your fingers the instructions say to check test point 22 reads 3.3 volts confirm another vital step disconnect the supply and short out JP for right now we'll finish off the display board if you left the mainboard headers until now you can attach the three males and three females together and place them onto both boards before soldering to guarantee alignment but if you're doing them separately like me just install the three male headers and as before tap one pin first and reseat to insure the headers are mounted flush against the board it's very difficult to correct this after all the pins are soldered now again being aware of heat buildup in any particular spot I also solder I'll turn the pins on the large header in two passes and as with the main board just make sure the two pin headers are aligned with the board edge alright you can now plug the boards together making sure the pins from all three headers engage and now in the big moment plugging the power supply and switch on the trace should be flat so try a finger test on the input probe and then the internal test signal and calibrate the probe you and that's it job done now if there are problems the instruction sheet has a troubleshooting flowchart and more test voltages just a quick look at the case this is trickier than I thought the assembly is not intuitive but there is a PDF guide on the internet now at first sight it looks to be really neat and precise but there's very little tolerance so several holes needed enlarging to stop the buttons and slide switches jamming and needle files are very useful here and here's how the sandwich of spacer place is meant to look but the oversized inductor messes that up so I left out one of the plates and just used extra nuts as spacers I also used more nuts either side of the mainboard to stop it flexing I do not over tighten the nuts and use washers if you have them to avoid any danger of the plastic cracking you can check the jye tech website to see what the latest firmware is mine was version 50 and at the time of this video the latest is version 60 so I bought the USB adapter and had a go at flashing and this worked perfectly so to summarize it wasn't all plain sailing but it's an interesting challenge and it kept me amused for a weekend along with all the videoing it cost less than a round of drinks so definitely a nice little project I want a slightly sour note the kit I bought may be a fake ripoff version I'm not checked with jye tech yet but even if it is there's not much I can do now apart from mention it so let's give it a quick test we've just used the multimeter as a power supply in resistance mode so let's connect it to the scope so it's definitely the red lead which is positive and it outputs just over three volts which agrees with what we measured earlier when we tested the electrolytic capacitors and what about those other DC power adapters I looked at here's one on load the Norton volt reference is one division from the bottom and it's two volts per division so this is about 10 volts with a fair bit of ripple and here's another one that's some ripple though turns out this one outputs a C naught D see so there are plenty of pitfalls if you can't see what's going on my intended use is for monitoring audio signals from a synthesizer so I'll finish by saying I hope this has helped and just fade out with a quick demo thanks for watching you you

Channel: Phil Tipping

Views: 207,224

Rating: 4.8998384 out of 5

Keywords: Oscilloscope, kit, diy, electronics, jyetech, multimeter, dso, dso-138 kit, dso138 walkthrough, dso138 build, storage oscilloscope

Id: 4Lsp5YZgsZU

Length: 22min 34sec (1354 seconds)

Published: Sun Apr 17 2016