In part two an ULN2023 is used so we can connect the IV-3A segments to 20V, while driving the segment with 5V. In this part the IV-3A is connected to the ULN2803A, and a 74LS48 which is BCD to 7-Segment Decoder. By using the 74LS48 we can use 4 bits to drive the 7 segments.
Connecting the IV-3A
To connect the IV-3A to the IV-3A follow the following table:
IV-3A connections
IV-3A
ULN2308
5
8
6
7
10
6
1
5
2
4
3
3
4
2
The last connections to make are the grid and heater. The schematic looks like:
IV-3A connections
Connect the 74LS48
The datasheet for the 74LS48 can be found here. Before connecting up the 74LS48, we need to invert the signals. Since the ULN2308 is a NPN Darlington array, we need to invert the signals, so that a segment is activate when the input signal is going HIGH, instead of LOW.
An easy solution is to use a HEX invert. Since a HEX invert, as the name implies has 6 inverters, so we need two of them. So 2x a 74LS04 is going to be used.
The schematic looks like:
Display Driver schematic
When connecting the all the BCD (248) inputs( pins: 76,2,1) to GND, the IV-3A should show a “zero”. Like wise, if we connect these pins to 5V, a 8 is shown. The table below show the BCD coding for the pins:
BCD (248) conversion table
A3
A2
A1
A0
Digit
0
0
0
0
0
0
0
0
1
1
0
0
1
0
2
0
0
1
1
3
0
1
0
0
4
0
1
0
1
5
0
1
1
0
6
0
1
1
1
7
1
0
0
0
8
1
0
0
1
9
In the next article the HP8175A is going to be used as a binary 4 bits counter.
In the first part I mentioned that I used 2 DC-to-DC converters. In this article we’re going to see how these modules are connected, and a ULN2803A is used to connect the segments to 20V, while driving the segments from a 5V rail.
Connecting the DC-to-DC converters
The connection of the DC-to-DC converters is very simple:This simple schematic shows how the modules are connected to the 5V rail.
One the modules are connected, the voltages needs to be set. This is done by turning a potentiometer. The XL6009E1 is set to +/- 20V while the HX-mini-360 is set to 1V.
Connecting the ULN28023
The ULN28023 is a Darlington array. Here you can find the datasheet.
The datasheet mention the following description:
The ULN2803Adeviceis a 50 V, 500 mA Darlington transistor array.The device consists of eight NPN Darlington pairs that feature high-voltage output swith common-cathode clamp-diodes for switching inductive loads.The collector-current rating of each Darlingtonpair is 500 mA. The Darlington pairs maybe connected in parallel for higher current capability. Applications include relay drivers,hammer drivers,lamp drivers,display drivers(LED and gas discharge),line drivers,and logic buffers.The ULN2803A device has a 2.7-kΩ series base resistor for each Darlington pair for operation directly with TTL or 5-V CMOS devices
So this IC is perfect to drive the VFD tube. Connecting the ULN2803 is simple:
In The next article the VFD tube is connected, and a 74LS48 is used to drive the the tube.
Creating vlans on a Juniper SRX is not as straight forward if you’re used to Cisco gear for example. In this article I hope to explain how to create:
One port as a trunk port
Other ports as access port
Add a mgmt L3 interface
Creating the trunk port
Let’s first create the trunk port. The interface fe-0/0/0 is used as a uplink port to another switch, and this ports carriers multiple tagged vlans. And it carriers only tagged vlans. No untagged vlan is allowed on this port.
To configure the port as a trunk port, the port-mode has to be set to “trunk” and the allowed vlans needs to be configured. In this case the tagged vlan id’s are: 100,102:
set interfaces fe-0/0/0 description UPLINK-BB-SLV-LAN-P1.0.12
set interfaces fe-0/0/0 unit 0 family ethernet-switching port-mode trunk
set interfaces fe-0/0/0 unit 0 family ethernet-switching vlan members vlan-102
set interfaces fe-0/0/0 unit 0 family ethernet-switching vlan members vlan-100
Note that the vlan names are used, which at this point still needs to be created. It’s also possible to specify the vlanid here:
set interfaces fe-0/0/0 description UPLINK-BB-SLV-LAN-P1.0.12
set interfaces fe-0/0/0 unit 0 family ethernet-switching port-mode trunk
set interfaces fe-0/0/0 unit 0 family ethernet-switching vlan members 102
set interfaces fe-0/0/0 unit 0 family ethernet-switching vlan members 100
Create the vlans
Creating the vlans is straightforward:
set vlans vlan-100 vlan-id 100
set vlans vlan-102 vlan-id 102
Create the access ports
Creating the access ports is just like creating a trunk port, accept the port-mode is set to .. yes you guessed it.. ‘access‘. So let’s assume we want to set the ports fe0/0/01 – fe0/0/7 as access ports with vlan 102.
set interfaces fe-0/0/1 unit 0 family ethernet-switching port-mode access
set interfaces fe-0/0/1 unit 0 family ethernet-switching vlan members vlan-102
set interfaces fe-0/0/2 unit 0 family ethernet-switching port-mode access
set interfaces fe-0/0/2 unit 0 family ethernet-switching vlan members vlan-102
set interfaces fe-0/0/3 unit 0 family ethernet-switching port-mode access
set interfaces fe-0/0/3 unit 0 family ethernet-switching vlan members vlan-102
set interfaces fe-0/0/4 unit 0 family ethernet-switching port-mode access
set interfaces fe-0/0/4 unit 0 family ethernet-switching vlan members vlan-102
set interfaces fe-0/0/5 unit 0 family ethernet-switching port-mode access
set interfaces fe-0/0/5 unit 0 family ethernet-switching vlan members vlan-102
set interfaces fe-0/0/6 unit 0 family ethernet-switching port-mode access
set interfaces fe-0/0/6 unit 0 family ethernet-switching vlan members vlan-102
set interfaces fe-0/0/7 unit 0 family ethernet-switching port-mode access
set interfaces fe-0/0/7 unit 0 family ethernet-switching vlan members vlan-102
However, this is a lot of typing. With junos it’s possible to use an interface range configuration. This is somewhat different to Cisco’s IOS or IOS-XE.
To use a interface range, first create a interface range name. For example ‘access-ports’. Then the name ‘access-ports’ can be used to add members. Next the properties of the interfaces can be assigned.
This might sound complex, but it’s quite simple and easy to use (and powerful):
set interfaces interface-range access-ports member "fe-0/0/[1-7]"
set interfaces interface-range access-ports unit 0 family ethernet-switching port-mode access
set interfaces interface-range access-ports unit 0 family ethernet-switching vlan members vlan-102
Assign the interfaces to the vlans
In the last step, the interfaces needs to be assigned to the vlans. So to assign the trunk port and access port to vlan 102 we need to do the following:
set vlans vlan-102 interface fe-0/0/0.0
set vlans vlan-102 interface fe-0/0/1.0
set vlans vlan-102 interface fe-0/0/2.0
set vlans vlan-102 interface fe-0/0/3.0
set vlans vlan-102 interface fe-0/0/4.0
set vlans vlan-102 interface fe-0/0/5.0
set vlans vlan-102 interface fe-0/0/6.0
set vlans vlan-102 interface fe-0/0/7.0
Note: the interfaces added are added by using the unit number, which is 0 here.
The above could be done in one command: simply by using the previous defined interface range ‘access-port’:
set vlans vlan-102 interface access-ports
When the an interface range is used, the trunk ports needs to be added as well:
set vlans vlan-102 interface fe-0/0/0.0
At this point the configuration can be committed:
commit
At this point, the layer 2 configuration is complete. The most easiest way to check if everything works is to look at the mac table. The command to do this is:
show ethernet-switching mac-learning-log
If everything is well it’s shows the learned mac addresses.
Create a Layer 3 management interface
To manage the SRX, it might be handy to have management vlan. In this case vlan id 100 is used.
To add a layer 3 vlan interface the next configuration is needed:
First create the vlan interface:
set interfaces vlan unit 100 family inet address 10.90.0.14/24
Next the interface can be added to the vlan 100:
set vlans vlan-100 l3-interface vlan.100
To activate to configuration don’t forget to do a commit:
Some time ago I figured out the pins of of IV-3A VFD tube. In the upcoming articles series I’m going to build a simple counter, and planning to use some of my LAB equipment to test and build this counter. Just for fun.
Roughly I’m thinking of planning the following articles :
Implement the PSU for the different voltages (1V,5V,20V)
Design and implement the display driver
Use the HP 8175A to simulate a 4 bit binary counter
Using a Hp8110A as a serial data generator to simulate a 4 bit counter
Finally build the counter
Implement the PSU for the different voltages (1V,5V,20V)
One of the first challenges when working with a VFD tube is getting all the different voltage rails required. The IV-3A tube needs the a couple of voltages: 1V,5V,20V
The get the 5V rail is not a real problem, 1V and 20V can be more difficult.
To start with the 1V rail, one might think of a simple voltage divider, but this is not as simple as it sounds. When trying to drive the heaters, this will add a load to the voltage diver. Which lowers the voltage, resulting in a voltage which is to low. This could be addressed by adding a opamp, as a buffer. However the circuit is going to get more and more complex.
So in this design I’m going to use small DC-to-DC converters. Or step-up converts to be more precise. And I use two modules:
One module to step up the voltage to 20v
One module to down convert the voltage to 1V
The modules ‘m going to use are:
XL6009E1
HX-mini-360
These modules are cheap, and easy to use.
The downside to this is that the heater could be driven “to hard”, on the other hand, these tubes can take somewhat of a “punishment”. I’ll keep the rest of the voltages low by driving the tube with 20V instead of the max 30V.
Both of the DC-to-DC converter modules are driven from a 5V supply. This makes it easy to implement the modules.
In the next article the display driver is going to be implemented.
After I repaired the Tektronix Bert tester PB200 I can finally do a test which I wanted to do for a long time. And that is to test the max data throughput of a breadboard. So in other words: What is the max speed at which data can travel through a breadboard (BB) without any errors ?
I came up with two tests:
The first test is to use a couple of rows on the BB
The second test is to use a power rail
Preparing the first test
The test setup is quite easy, just a few wires on a bread board. I didn’t put the wires across the whole length of the BB, at that point a lot of other stuff comes into play. Just by adding a few wires I get (roughly) an idea what the impact of extra connections is.
And to get an initial impression I started the test with just connecting the probes to a BB and measure the data transfer. This gives me a base line of 80 Mhz.
Next I prepare the BB as follows:
As can be seen just a couple of connections to generate some contact resistance. The BB and wires will add some capacitance too.
The test results of the first test
This results in:
It’s somewhat hard to read from the reflecting screen, but the max throughput I got after running this test for a couple of hours is around 77Mhz. So compared to the earlier test, adding a couple of wires resulted in a loss of 11Mhz. Which is quite a loss.
But note that this is is quick test. I didn’t use a loaf of 50Ohms, and I used a good quality BB (BusBoard Prototype Systems BB830).
Setting up the second test
The second test looks like:
Once this is setup I ran the test. When a test fails it looks like:
When an error occurs I lower the frequency, and reset the error. And the end
Results of the second test
I could get a max throughput of:
So it’s very close to 80 Mhz. However in a real case scenario don’t expect to send data across with this high speeds. In reality I ques somewhere around 10 Mhz till 40Mhz is more realistic.
Playing around with the R&S SMT03 and an HP8591A Spectrum Analyzer
Now that I fixed the R&S SMT03 I find finally time to play around with the SMT03. The idea is to learn more about modulation, and how to display this on a Spectrum Analyzer. In a previous article I used the Siglent SSA 3021X Spectrum Analyzer in this article I’m going to use a HP 8591A Spectrum Analyzer.
Preparing the R&S SMT03
First off I need to setup the R&S SMT03
I’m going to use a carrier signal of 100Khz, and AM dept of 27%. And since the SMT03 have a second LF Generator I use that one to generate a sinus wave of 1.000 Khz. To protect the input of the HP SA I set the amplitude to 0 dBm.
Setting up the HP8591A Spectrum Analyzer
After setting up the R&S SMT03 it’s time to configure the HP8591A
After setting the center frequency the SPAN is set to 20 Mhz. To see the AM modulation, a smaller SPAN is needed. After the SPAN is set to 1.5Mhz the AM modulation becomes visible:
This shows the AM modulation. I really like the HP 8591A SA, it has a easy to use interface. And having a R&S SMT03 and the HP8591A in my lab is really awesome.
Understanding the difference between Oscilloscope and Spectrum Analyzer
Before diving into the use of a Spectrum Analyzer (SA), a short explanation between an Oscilloscope and a SA might be handy. If you used a SA before, this article might not be to any interest to you, since this article covers a basic understanding.
For those who a curious to what a SA is, hang around, since this article is about to demonstrate the difference between a Oscilloscope ans a SA.
When starting with electronics, sooner or later you might find yourself wanting an Oscilloscope to look at (fast) changing electronic signals. In other words: An scope is a multi functional tool in a electronics lab, and every good electronics labs should have one. With a scope it’s possible to look at electronic signal, being it digital signal or analogue signal which changes over time. But a scope can also be used to measure voltages, and all other characteristics of a signal. For example, the fall and rise time of edges, period of a signal, the max and min voltages, and perform math functions on signals.
Using a Oscilloscope to look at a signal
Most often a scope is used to look at a signal, and see how it looks like. For example a sinus signal:
Looking at the signal we can tell that the signal is 50mV (Peek to Peek), and that the frequency of the signal is 100Khz. Looking at the signal closer, it’s not a sharp clean sinus signal. So what’s wrong ?
If we zoom into the signal to have a closer look, the signal looks like:
This is doesn’t look like a clean signal. At this point several things may be the cause:
Is there something which interferes with the signal?
Is the measurement done properly (aka signal integrity)
This is the point, where it’s very difficult, to use a scope to investigate this further. Just let’s assume that this is no measurement fault. Short ground leads are used, and the probes are calibrated.
That leaves us with a interfering signal of some kind.
How to determine what kind of signal this is?
What is the frequency of this interfering signal ?
At this point some want’s to use a feature which is called “FFT” which some scope might have. FFT stands for: Fast Fourier Transform spectrum analyser When using this feature the scope is behaving like a SA.
Having a FFT feature on a scope might be handy, in my case the FFT feature on my Rigol Ds1054Z is not very helpful:
It shows that there seems to be an extra signal, but it’s not possible to get any detail on this signal. To get more detail, a real Spectrum Analyzer is needed.
What is a Spectrum Analyzer (SA)
A Spectrum Analyzer might at first glance be some kind of a scope. It has a display to show signals, and has a lot of buttons, like a scope.
However the main difference between a scope and SA is that:
A scope shows signals in the time domain
A SA shows signals in the frequency domain
This means that a SA show on the horizontal the frequency, and on the vertical the power of the signal, which is shown in a Logarithmicscale. This can be for example in dB or dBm. The reason for displaying the power (on a scope you would say the amplitude) of the signal in a Logarithmic scale is that low power signal can be displayed next to high power signals.
And since a SA displays signals in the frequency domain, it’s possible to see how “pure” or “clean” a signal is, since we can actually look at the “spectrum” of the signal. Hence why it’s called a “Spectrum Analyzer”.
Using a Spectrum Analyzer to look at a signal
Let us look at the same signal which we looked at on the scope, but now feed into a Spectrum Analyzer:
Here is the same signal, but it looks quite different from the signal which is shown on the scope. However it’s frequency is 100Khz, and the power of the signal is -46.00 dBbm. Which is about 3.169 mVpp (There is some loss in the cables, and adapters used).
Looking at the signal it’s seems “not clean”, But it’s hard to see. So like on a scope, it’s possible to zoom into the signal, and get more detail. To this we need to set a smaller SPAN. The SPAN on a SA is the bandwidth were we are looking at it. It’s like the zoom-lens on a camera, by zooming in, more details are visible. Currently the SPAN width is 20.000Khz.
If we change the SPAN width to let’s say 1.000Khz, we see the following:
And suddenly a second signal appeared. To get more details about this signal, the SA provides a easy way, and that’s by placing a marker. In this case a delta marker is used. A delta marker can show the difference (delta) between signals.
And then we see that the interfering signal is a 100Hz away from our original signal of 1oo.ooo Khz signal. So the interfering signal is 100.1 Khz.
Conclusion
And this shows the difference between a scope and a SA. An SA is a very handy tool when looking at the spectrum of a signal. It’s how every a more complex, and sometimes more confusing tool to use. On the other hand, a scope is also a complex tool to use. But in general, a scope is much more used for looking at signal then a SA. A SA is mostly used when dealing with RF, radio’s transmitters and alike.
Before diving into repairing the Tektronix PB200 BERT tester, let me explain briefly what a BERT Tester is. BERT stands for ” bit error rate test ” In the most simple form, a BERT tester sends out a random bit patron, and an analyzer receives the bit pattern and compares this bit pattern to see if there is any bit error.
Obviously this is more complicated, how does the analyzer now what the original bit stream was ? The theory behind it this is quite complex, and beyond the scope of this article. For a more in depth explanation see [this] Wikipedia article.
A device like the Tektronix PB200 is used to test different data transmission devices, like optical interfaces, or a like.
The Tektronix PB200 has a data generator and an analyzer built into one device. The specs for this device:
GENERATOR
Clock Frequency: DC to 200 MHz.
Amplitude: 0.5 to 5.0 V p-p.
Termination select: 50 Ohm to -2 V, +3 V, AC or GND.
Input range: ECL, TTL, PECL compatible.
Threshold resolution: 10 mV step.
Internal synthesized clock source: Frequency: 1 Hz to 200 MHz.
Error injection: Error: Single, Rate, External (TTL).
Field select: Overhead, payload or both.
Error rates: Error rate of 10-n, n = 3, 4, 5, 6, 7.
Outputs: Data and clock outputs:
Format: NRZ.
Configurations: Differential (True/Complement).
Source impedance: 50 Ohm.
Amplitude: 0.5 V to 2.0 V, 10 mV step.
A Tektronix PB200 which is dead
Before I can play around with this PB200, the device needs a repair. I bought this device as a “none working, for parts”. And well.. it sure is in a “none working” condition, since the device doesn’t power on, at all.
That is one of the reasons I bought this device. When a device is not able to power on, this normally means the Power Supply (PSU) has a problem. The downside of this is of course that their is no easy way to test the rest of the functionality of the device.
Assessment of the problem
Once the devices arrived at my doorstep, I could inspect it further. And I noticed a sharp bent in the front panel once I removed the covers. Not a good sign to start with. The second thing I ran into is that this device is a complete nightmare to take apart. The construction is just horrible. Screws on places which are heard to reach. I suspect this is just a branded by Tektronix. I got my hands on some Tektronix equipment, and repaired some, and the construction is always good engineered. In this case, it’s definitely not.
So it took a lot of effort to get the PSU out of the chassis. Once the PSU was out I noticed a burned up diode, and a burned spot on the PCB. A quick check of the fuse confirmed: This PSU had a very bad moment. This means that on the primary side of the PSU a lot of other components could be damaged. So the first thing I did was to hunt for a Service Manual, and well these cannot be found.
So I started to de-solder the diode, so I could get a marking of the component. The diode was next to some transistors, or MOSFETs so I decided to desolder them as well, since they are most likely also damaged , or are the cause of the damage.
While taking the diode out carefully, I could not prevent it from falling apart.
The diode literally exploded and split into halve. With a lot of trouble I managed to get some marking, but I wanted to make sure that I got it right. Primary side of a PSU always makes me nervous. So I started a [thread] on the EEVblog forum.
Another member also suggested to get a PSU replacement, which is almost the same. The only difference is the output voltage.
So I decided to buy this PSU, so I have a reference, and if I’m unable to repair the primary side of the PSU I could perhaps convert the secondary side so it gives the right voltages.
I started to measure and test several components, and found some diodes which where shorted. Replaced them. However I could not measure any voltages after the full bridge rectifier. Some components are mounted on large heat-sinks. Removing them to get access to the components and be able to read the markings or to test them out of circuit, would be a pain.
Fighting with this power supply for a couple of evenings, I decided to take another route. In the meantime the alternative PSU was delivered. After comparing both the PSU’s together I noticed that only one voltage rails was different.
Modifying an PSU
Since fixing the primary side of the PSU would be very difficult to do, I started to look at the secondary side. Both the PSU’s are from the same series. So I figured the manufacturer probably used a couple of zener diodes, and resistors to control the output voltage. So I started to swap out diodes and resistors which where different and which I could relate to the voltage rail I wanted to adjust.
The moment of truth
I powered to PSU up, and measured all the good voltages (they where a little higher, but that’s okey since no load is attached.). I decided to go for it, and placed the PSU on top of the chassis, so I could test the PSU without going through the rather complex method of installing the PSU.
And after connecting the main power, and flipping the power switch, the PB200 came back to live.
A few quick tests showed me that the generator and analyzer are working without any problems. And I refitted the PSU back into the PB200.
The R&S SMT03 is a RF signal generator which can generate signals from 5Khz up to 3Ghz, while the signal level can be from -144dBm to +13dBm with 0.1dBm resolution.
Signal generators like the SMT03, and other (for example the HP ESG series like the E4421B) are mainly used to test communication devices and a like. Signal generators like this, are not arbitrary signal generators (however they may have an option to generate LF (Low Frequency) signals like square, sine, sawtooth wave-forms.
RF Signal generators generate sinus signal, and can generate different modulations (FM,PM,AM etc). These signal generators are a specialized piece of equipment.
An R&S SMT03 with problems
The SMT03 I’ve got in the LAB has some problems:
A few lines are visible on the LCD screen
When the unit is on for some tine, above 1.8Ghz the error: 110 Output Unleveled ALC failure is displayed .
The lines on the LCD screen are somewhat annoying, they don’t influence the working of the unit. The ALC Unleveled error does. When I try to measure the signal, the level is all over the place, and has a low level. I noticed that in the short time this error is not present I can loose up to 4dBm when I generate signal above 1.8Ghz.
The challenges
When trying to fix an error like this, it’s important to understand the error. At the time this error presented itself, I didn’t had access to a Service Manual. And from the User manual I didn’t got any wiser. So after some thinking I concluded that ALC must stand for: Attenuation Level Control
This leads me to the conclusion that a possible cause could be a PLL circuit which is unable to establish a successful lock. The bad news is: this may be due to a lot of other problems:
The input frequency may be of, or the signal is to low
Power problem (low / not working power rail
Mixer problem
And a lot of other related problems
Trying to diagnose the problem futher
So to diagnose such a problem, a block diagram and a schematic would be very helpful. But I got neither of them.
Another challenge is that the unit consists of modules, which plug into a back-plane. Operating the modules outside of the unit seems only possible with a “service kit” which I don’t have access to, and cannot find any information about.
Despite the fact I don’t have the above items, I can observe the error, and take a look at how the physical signal path. So I opened the unit by removing the covers. Which is a simple and straightforward process: By unscrewing the bumpers on the back of the unit the top and bottom covers come off.
R&S SMT03 on the inside
Tracing from the output connector the signal path back I noticed that:
From the output connector, the signal is going through an attenuator, and then straight into a 3Ghz module (W154).
From the 3Ghz module the signal is entering an 1.5Ghz module (W104).
From this module the signal is going to a synth module, and a signal generator module.
And this tells me that the 3Ghz module has some kind of “pass-through”, so that signals up to 1.5Ghz are passed through the 3Ghz module (not sure at this point if some additional filtering is done). When signals are above 1.5Ghz the 3Ghz module generates the frequencies from 1.5 till 3Ghz.
This could mean that the ALC Unleveld error is somewhere in the 3Ghz module. Which means I could leave all the other modules alone.
For a moment I was thinking about a possible power rail problem, however this is most unlikely, since I aspect that for every frequency the ALC Unleveled error should be displayed, or that other errors would pop-up.
To summarize
Working on these units is not easy
A Service manual would be a great help
In [part 2] I’m going to try to repair this R&S SMT-03
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