Simple Voltmeter schematic using Maxim’s ADC with LED driver

MAX1496 is an ADC with internal 31/2 digit LED display driver. This is an ideal IC for simple voltmeters. You just need the IC, and a couple more components and you are done. The following is a circuit I made using EAGLE. This is kind of a knock off circuit I built after going through the datasheet.

Voltmeter using MAX1496

All the controls are connected to a 10pin FRC which is to be hooked to a microcontroller to automatically set the ranges. RJ1 and RJ2 controls the LED drive currents. They are made as female pin headers to insert resistors. More details will be added soon…

Datasheet : MAX1496, MAX1447, MAX1498 datasheet

Posted in Test and Measurement | Tagged , , , , | Leave a comment

USB Microcontroller Programmers and Laptop RAM

After wasting a lot of time, I finally made the OpenProg. The whole deal was much easier because I had already built the USBPICprog. OpenProg is not just another programmer, it will program Microchuip’s PIC micro-controllers, Atmel’s controller and read and write to EEPROMS.

Last month I got another 1Gb strip to the already outdated Compaq C770TU laptop. Things didn’t go very well as transcend now ships modules with 1Gbps chips instead of the older 512Mbps chips. So now my laptop randomly fails to boot unless I press some key. Here is a small video of me tweaking around with it.

[youtube]http://www.youtube.com/watch?v=Wj3mA0Kizhk[/youtube]

Coming back to the programmers, I now have two of them. The USBPICProg one and the OpenProg. Although I have used my USBPICprog many times, I didn’t get a chance to use the new one. In the mean time, here is a picture of the two programmers mating ;)

USBPICPROG and OpenProg , OpenProg has got a USB type B connector while USBPICprog just has broken Sony phone data cable

The broken Sony Erricson USB cable was the only one available at the time I built USBPICPROG. On the OpenProg the USB type B is not sitting on the mainboard because of the difference pitch. OpenProg firmware was burned into the PIC18F4550 using USBPICPROG.

The Adapter board is used to program PICs, all of them 40, 28, 20, 18, 14 and 8pin.

The adapter board just allows to plugin all types of PICs into one single ZIF socket. More about both of these programmers will be coming in detailed posts.

Posted in General | Tagged | Leave a comment

PWM chip CG8010DX16 SMPS schematic and datasheet

A few days ago, one of the readers – Murugesh had commented asking for help to identify an IC he had with him. He sent a picture of it to me. I was not able to identify the IC on my own. I turned in to the amazing fellows at edaboard and got two correct answers within an hour. Thanks foes to those two wonderful people. Here is a link to the thread on edaboard.

Here is the picture Murugesh sent me (All the copy rights or copy lefts belong to Murugesh ;) )

PWM chip photograph

PWM IC CG8010DX1 - SMPS chip used mainly for Desktop PCs

The IC turned out to be a PWM IC used for PC Switch mode power supplies. while composing the post on SMPS circuit diagrams, I had actually came across a circuit with this particular IC, but ignored for it being not so popular. But the guys at edaboard even posted a link to that circuit diagram.

Circuit diagram of PC SMPS using IC cg8010dx16

Downloads

I have downloaded and attached the datasheet of IC CG8010DX16 – PWM controller.

Posted in IC | Tagged , , | 4 Comments

Op-Amp based voltage regulator tutorial and SPICE modelling

The tutorial is taking a long time. In the mean time here are the screen captures, schematic and the LTSPICE files.

LTSpice schematic of a simple op-amp voltage follower based Linear Voltage Regulator.

Downloads

Op-Amp_linear_voltage_regulator SPICE files

Posted in Linear | 2 Comments

New multimeter – Extech EX430

My multimeter of 8 years a Mastech M92A had lost its accuracy. I was in dire need of a new multimeter. Here in India, all the Flukes and Extechs cost double of what its worth in the US or Europe. So I got one from the US by my cousin. The new DMM is an Extech EX430 true RMS multimeter with Temperature, Frequency/Duty cycle and Capacitance measurements. A review is on its way. In the mean time here is a snap :)

The new Extech ex430 true RMS multimeter

Posted in General | Leave a comment

Design : Linear Voltage regulator using Op-Amp Voltage follower

The Laptop was down for a couple weeks because my dealer couldn’t get me a replacement for the broken power supply. Although I had a friends laptop, the unreasonable delay got me quiet frustrated. In fact it pushed me so hard, I decided to build a ‘Linear’ power supply for temporary use. This meant I would have to design (kind of) one all on my own. The good thing is, I learned a lot and the bad thing, I still had to wait till I got the original PSU, to turn the laptop on.

So why not a Switching PSU instead of the Linear one?

  • I have zero experience designing a switching power supply
  • I do not have a ‘properly’ working DMM :P
  • Linear one is much easier to build and I had components lying around
  • Although I haven’t yet designed any Linear PS, I was pretty sure they would work real good

And off I went got a piece of paper and started scratching my head!

Linear Power Supply constructed using an op-ampFully assembled power supply. The heat sink is pretty big, but its no match for the large amounts of heat the transistor dissipate.

Design scribble for voltage regulator

The scribbled diagram is not correct. It's purpose was to get a basic idea to work on.

Theory:
The series regulator is a simple extension of the voltage follower circuit of an op-amp. In simple words, an op-amp always tries to adjust its output so as to make both the inputs equal (inverting and non inverting). (the concept of virtual ground is used here). Since an op-amp cannot provide much current a series dissipative element, an NPN transistor, is used. The one I used is a 5Amp TIP122 Darlington transistor.

If we increase the bias to the base Vbe of an NPN transistor voltage drop across it Vce decreases (as Vbe increase, Vce decrease). When the whole circuit is wired up and if the output voltage increases due to some reason, this should be compensated by an increased voltage drop across the transistor (Vce). For this the base bias Vbe should decrease. This means the output voltage should be multiplied with a scaling factor and negatively fed back to the base of the transistor. This is where the op-amp comes to play. The output through a potential divider is connected to the inverting pin of the op-amp.

To get a stable output voltage, we need a reference source to compare the output voltage to. For this purpose, a simple Zener diode and a series resistor is used. This acts as a pretty good reference source. The reference voltage is connected to the non-inverting pin of the op-amp. This is because, we need to get a positive correlation between reference voltage and the output.

5A NPN darlington Transistor TIP122-D

Posted in General | Leave a comment

Breaking in – Compaq C770TU laptop

My laptop is a Compaq C770TU which has been out of service for some time because of a faulty power supply. I tried to build a power supply temporarily due to delay in acquiring a new one. The plan was dropped because of design problems faced (a post s coming soon). so last day I go my power supply and switched it ON and did some stuff. Everything was going fine, then it switched off all of a sudden. The most likely cause would be overheating (thermal shutdown). All the computers today have an automatic thermal shutdown so that the processor will not get damaged. As expected the bottom side was red hot and being so curious I decided to open my favorite laptop to see what was wrong with the fan.

The problem being with the fan was kind of obvious. And off I went, grabbed a screw driver and kept taking things apart until nothing was left to fall out. The heat dissipation system is interesting. A large Copper bar is pressed on to the processor and this runs along the inside of the body to the air vent. There, a window with fins is attached to the copper bar (the fins are probably Aluminum but I am not sure). This is at the exit of the centrifugal blower. The pictures will help in easier understanding.

DSC01900.jpg

The fan is held by just one screw. After the fan is just pulled up, the heat fins connected to the copper bar coming from the processor can be seen. (The copper bar is also seen here) This is clogged with dust.

DSC01901.jpg

I have already removed a small mass of dust and lint from the blower side of the fan. This is a centrifugal blower.

The blower and the fins fitted on the heat bar was full of dust and this prevented the blower from rotating. A large painting brush was used to remove the dust. The blower was connected to 5V supply and tested. The sound is really good to hear. especially when it is outside. Blower has a rating of 320mA @5V. Opening the laptop is pretty much easy if you have got the right tools. Most of the time a Philips screw river and a flat one would suffice. The flat one used to unclip the tabs. Only thing you need to care is not to break any of the clips and not to loose any screws you take off.

Posted in General | 1 Comment

PC SMPS schematics with IC 2003 and TL494

What would you do if you have got a couple broken Switch Mode Power Supplies, a screw driver and some curiosity!? Well obviously you would crack it open and try to figure it out. I have to admit, we would probably have opened them before they were even broke. That is exactly what I did.

[sc name="begin_of_toc"]

  • SMPS schematic using IC2003
  • SMPS schematic using IC KA7500
  • SMPS schematic using TL494 and LM339
  • Datasheets
  • Links
  • [sc name="end_of_toc"]

    When I had a couple of them lying around, I cracked them open and after a few days, fixed some of them. It was actually much easier done than said. But one bad thing about SMPS repairs is that there aren’t any good resources out there on the web. (OK may be there are, but I failed to find some). That is why I decided to make a series of posts with my repair notes, schematics and stuff I have learned through opening those bricks. Being the first post, this is the schematic post. You can grab the schematics available on the net here. Please send me a link if you have found a new schematic and I will add it here.

    The Schematics

    There are two circuits commonly available for PC ATX SMPS.

    • Based on IC2003
    • Based on KA7500
    • Based on TL494 and  LM339

    KA7500 and TL494 are pin to pin compatible PWM controllers. There are only minimal differences in their specs. The major difference being for the TI one TL494 DTC offset voltage is 0.1V where as for KA7500 it is 1.2V.

    Thanks goes to : http://electro-tech.narod.ru

    PC SMPS using IC2003

    SMPS schmatic using IC2003. The cheap Chinese SMPS uses a circuit based on IC2003. The EMI filter and output filters are usually left out, and the components heavily underrated. The schematic is hard to find, not drawn by me.

    This schematic along with the low quality parts is normally seen in Mercury branded SMPS. I have 6 of those lying around. All with blown caps and no EMI filter. EMI filters are not much of a concerns usually for ratings below 350W. But a good engineer /designer will always add an EMI filter.

    The manufacturer has omitted this along with output filter coils to cut costs.

    SMPS-Inductor-repair-2003-schematic.JPG

    Here is an SMPS based on IC2003 after repairs. I found some inductors to add to the output filter, but couldn't find any for the EMI filter at input.

    SMPS schematic using IC2003

    SMPS schematic using IC KA7500

    ATX-SMPS based on TL494 and LM339

    The TL494 LM39 combination was the most widely used one till recently.

    Click on the images to enlarge. If you know anything about Switching Power supplies, the schematics are quiet obvious. They are simple. Include simple protections and have very few components.

    Datasheets

    TI PWM controller datasheet – TL494 | Fairchild PWM controller – KA7500C | National’s Quad Comparator – LM339

    Product page of TI’s TL494 | Product page of KA7500 | Product page of LM339

Posted in Switching | Tagged , , | 39 Comments