Jyetech Digital Oscilliscope
by Matthew Ford 20th June 2009
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Displaying 62.5Khz square wave
The JYETECH Digital Storage Oscilloscope arrive last Wednesday. Cost US55.00 assembled with front and back panels, universal power supply (American plug) and clip leads and including registered post.
It is about the size of a packet of cigarettes with a screen about the size of a match box and very light, as is its external power pack. With the front and back panels it feels sturdy, but not having any side covers you will want to keep it in plastic bag when not using it.
After bending the plug pins so that they would fit in an Australian socket, I powered it up. After briefly displaying an initialisation message, the oscilloscope screen comes up. On the left hand side are three switches, the bottom one lets you select AC, DC coupling or Freq. The middle switch lets you ground the input or select the 0.1V or 1V range. The top switch set the vertical multiplier, x1, x2 or x5 for 0.1V, 0.2V 0.5V per division on the 0.1V range and 1V,2V,5V per division on the 1V range. The display has 6 vertical divisions, so the maximum voltage waveform you can display completely is 30V pk-pk. The smallest voltage difference you can see is 10mV as there are 10 dots per vertical division on the screen. The input bottom left banana plug is marked as 50Vpk Max.
There are 10 horizontal divisions shown on the screen. This is a window on the whole sample of 26 divisions. The first 6 divisions show pre-trigger wave form.
On the right hand side of the front panel are click buttons to adjust Vertical postion of the trace, horizontal position of the window on the sample, the sec/div can be adjusted from 10mins/div to 5uS/div (i.e. 260min wave form capture to 130uS wave form capture) Each wave form capture has 256 samples or about 10 per horizontal divison which is also the number of dots per horizontal division. You can also select the trigger mode, Auto, Normal, Single shot, the trigger slope, rising or falling and the trigger level, indicated by as small arrow head on the right of the grid. Having selected one of these controls, you use the + and - buttons to make the adjustments. The selected control is highlighted at the right of the display grid.
The OK button functions as a HOLD button for Auto and Normal triggers and as a reset capture button for the Single shot mode. Holding the OK button down for 3 sec switches to Freq. mode. To get a frequency reading you also need to change the AC/DC/Freq switch to Freq. The frequency seems to sample about once per sec. To return to the oscilloscope function, press the OK button again for 3 secs and move the AC/DC/Freq switch off the Freq setting.
There is 500Hz 5Vp-p test signal provided at the top left. On my unit the test loop had been push back onto the mounting pillar and the multiplier switch body. Both these seem to be electrically floating but I just straighten the loop out in any case.
In the top middle of the unit is a small heat sink which gets noticeably hot to touch. While it is uncomfortable to hold, it is not hot enough to burn.
The buttons some times do not register your press, but + and - buttons will repeat after a short time if you hold them down. In all cases I found it easy to change the settings to what I wanted. Although some times it took an extra press or two. The horizontal and vertical adjustments can easily be made in 1/10th of a division, the finest display resolution.
The instructions come on a single double sided A4 sheet and can be downloaded from https://www.dpcav.com/data_sheets/DN062-06v02.pdf
I tried using the frequency meter mode to measure the uC 8Mhz clock. In frequency mode the oscilloscope is only rated up to 5Mhz but mine measured 8Mhz as 8011635Hz varying by +/- 8.099Mhz to 8.015Mhz My multimeter, which claims 0.05% accuracy, measured 8.00Mhz flashing to 8.01Mhz. So the frequency is quiet accurate as you would expect from a crystal controlled device. In contrast 50Hz hum is shown as 50Hz (2 digits only) so you lose display resolution as the frequency decreases.
Here is a screen shot of a 4Mhz reading
DC accuracy also looks good, I measured a fresh battery with my multimeter, 1.607V, the oscilloscope on the 0.1 x5 DC range read 1.6V +/- 0.1V display resolution.
The bandwidth is quoted as 1Mhz, but for digital applications you can clearly see the effect of the input filtering on a 62.5Khz square wave. The leading corners are rounded off as is shown in the photo at the top of this review.
Below is the Jyetech display of 62.5Khz
Here is the display of the same signal on Tektronix TDS1001 which has a 40Mhz bandwidth, after checking the probe compensation.
This shows the signal as a very clean sharp edge with some overshoot.
The rounding of the rising and falling edges on the Jyetech is solely due to its reduced bandwidth. The Jyetech only has clip leads so there is no probe compensation adjustment for it. The fastest time base is 5uS so a 100Khz square wave signal is about the upper limit of this unit. This fits with engineering rule of thumb, "have a cut-off frequency about 10 times your signal".
Occasionally the screen would go blank when I lay the unit down. I needed to power down and up to restore it. Also during this photo shots the frequency reading dropped and later the square wave did not display correctly. Looks like this unit has some dry solder joints. When I get a moment I will take off the panels and run an iron over all the joints. The Horizontal postion movement only works when you are HOLD mode. When not in hold the +/- buttons don't scroll the display. Not a problem. It just took a little time to discover why I could not scroll.
If I could have one extra feature it would be an external sync input. 0V to 5V would be OK. This would greatly improve the usefulness of this unit in debugging uC outputs.
I would recommend this unit to any one working with electronics who has a multimeter and cannot justify spending hundreds of dollars on an oscilloscope.
Even if you have a full sized digital oscilloscope, as I have, the size and weight make this unit makes it a much more convenient tool to take anywhere you would take your multimeter.
The Jyetech website lists a number of distributors or you can order from them. I ordered mine from http://www.seeedstudio.com , their shipping was cheaper. You can also buy this unit as a kit for a lower price.
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