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- DELAYED_SWEEP_ADAPTER
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"Delayed Sweep" Another feature of most good scopes is "Delayed Sweep." Delayed Sweep, allows the user (that could be you, if you behave and eat your vegetables) to trigger on an event and observe the signal after some predetermined time interval. For example: if you wanted to observe one single scan line--out of 525--in a television signal, you would trigger off of the beginning of each television field time (16.67 msec) but holdoff displaying that particular scan line (HD = 63.5 usec) until the correct amount of time has passed. In essence the Delayed Sweep is just a fancy "One-Shot" multivibrator with a ten-turn pot, triggered from the scope's normal sweep circuit; and holds off the sweep across the screen until some time interval--determined by our old friends Ms. R & Mr. C--has passed, after which time the scope sweeps for the interval of one TV scan line. |
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Numbers Don't Lie... People Do: Let's say I wanted to eyeball the 188th horizontal scan line, and I had dialled in both the "Delay" and the "Sweep" intervals: as soon as the field sync pulse (VD) occurs the delay sweep starts to time out for 11,885 usec (187 x 63.5), at which point it triggers the scope's sweep generator. The sweep runs for ~ 65 usec--displaying one complete horizontal scan line (the 188th). Other features of the oscilloscope that are available, are left for the user to discover in the user's manual: you know, that thing you read when "all-else-fails!" |
DELAYED_SWEEP_ADAPTER
The schematic for the delayed sweep adapter is shown in the figure. Power for the circuit is pro-vided by a dual-polarity, 5-V supply. An LM360 high-speed comparator (IC1) with complementary TTL outputs is at the heart of the circuit. A trigger-level control, potentiometer R2, allows the adapter to trigger on any part of the waveform being displayed. With the values shown, the circuit functions well with a Hitachi V-212 oscilloscope, whose channel 1 output is about 25 mV per vertical division of the signal display. Assuming a normal display of about six divisions, the level control pro-vides a range of ±150 mV. You can change that range to suit your scope output by adjusting the ratio of R3 (15,000 Ω) to R4 (470 Ω); however, maintain the ratio of R5 (100,000 Ω) to R4 (470 Ω) for proper hysteresis. Resistor R1 (51 Ω) terminates the 50-Ω cable from the channel 1 output jack. IC2, a 7473 TTL dual J/K flip-flop, is configured in its toggle mode to divide the input frequency by 2. That ensures that IC3, a 74121 TTL monostable multivibrator, will function accurately over the in-put waveform's full time period. The pulse output from IC3 is coupled to the trigger-input jack of your oscilloscope, and the slope is selected via S2 to match the slope selected on your oscilloscope. Po-tentiometer R9 allows fine positioning of the trace and potentiometer R7 allows the output pulse width selected to be multiplied by a factor from x1 to over x2.5. Switch S1 lets you select the de-sired pulse width by switching in C8 through C13, in a 1-2-5 sequence. The adapter circuit was de-signed to operate on an external ±5-V, 100-mA power supply to avoid 60-Hz pickup in the unit.
http://www.electronixandmore.com/projects/simplescope/index.html
The XYZ scope becomes an oscilloscope with the addition of a sweep circuit, which could be simple or incredibly intricate. The Version 2 TV-to-Scope converter already has two sawtooth sweep circuits for the vertical and horizontal. We only need the horizontal and the speed can be adjusted in ranges by changing the capacitor size. The 555 timer is limited to sweep speeds of up to 500kHz (LMC555 – 3MHz ILC7555 – 1 MHz) ; different components and circuitry would be necessary for faster sweep speeds. Below is a schematic of the sweep circuit to transform the XYZ scope into a simple oscilloscope. The +5V supply for the sweep may be derived from the XYZ scope supplies.
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The sweep circuit has basic triggering to synchronize the sweep to the amplified vertical axis signal from the op-amp. Due to the simplicity, the triggering does not always have a perfect lock on certain signals but it does reasonably well for a simple RC circuit.
http://gsuryalss.wordpress.com/tag/operation-principle-of-sawtooth-wave-generator/
The sawtooth wave (or saw wave) is a kind of non-sinusoidal waveform. It is named a sawtooth based on its resemblance to the teeth on the blade of a saw.
Click the image to enlarge…..
Sawtooth wave generators using OP-Amp are very common. But the disadvantage is that it requires a bipolar power supply.
A sawtooth wave generator can be built using a simple 555 timer IC and a transistor as shown in the circuit diagram.
The working of the circuit can be explained as follows:
The part of the circuit consisting of the capacitor C, transistor,zener diode and the resistors form a constant current source to charge the capacitor. Initially assume the capacitor is fully discharged. The voltage across it is zero and hence the internal comparators inside the 555 connected to pin 2 causes the 555′s output to go high and the internal transistor of 555 shorting the capacitor C to ground opens and the capacitor starts charging to the supply voltage. As it charges, when its voltage increases above 2/3rd the supply voltage, the 555′s output goes low, and shorts the C to ground, thus discharging it. Again the 555′s output goes high when the voltage across C decreases below 1/3rd supply. Hence the capacitor charges and discharges between 2/3rd and 1/3rd supply.
Note that the output is taken across the capacitor. The 1N4001 diode makes the voltage across the capacitor go to ground level (almost).
The frequency of the circuit is given by:
f = (Vcc-2.7)/(R*C*Vpp)
where:
Vcc= Supply voltage.
Vpp= Peak to peak voltage of the output required.
Choose proper R,C,Vpp and Vcc values to get the required ‘f’ value.
Вариант ГПН (переделка из ПНЧ)
Заменить R1 источником тока, пилообразный сигнал снимать с выхода ОУ через составной истоковый повторитель. С вывода 3 таймера, через конденсатор, сигнал гашения ОХ (но лучше ОХ гасить триггерной схемой – нет коллизий по постоянной времени схемы гашения и временем ОХ.
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