ICL-7135 Based 4-1/2 Digit LED Meter

v just pay attation to your reference source!

Ooowww yes of course I have.... and its not just the reference you have to pay attention to, its the layout digital and analogue grounds etc... as well as the selection of integrating and autozero capacitor - you can't just bung a polyester in and hope it works as an ideal capacitor...

Must use polypropylene or other very low dielectric absorbtion type of capacitor...

Then there's the resistors and so much more... Oh as well as the reference!!

John.

Hello John

Nice to see you again.

Is there some one who can do all that and for so small money for me. Perhaps I can think of taking 100 meters. I am afraid of putting hand in this. Will he result be any better than those 24-bit delta sigma? I have used ADS7813 of Texas 16-bit and it is stable only for 4-digit with +/-1 count change / C. This was too much for me as room temperature here changes a lot (easily 20C). It kicked the last digit in drift.

I am planning to keep travelling to USA in 2007 and 2008 so can drop on the way to ship some white wine with you. Are you ready? My daughter from UK is coming home in Feb so I may keep away from CR4. We will like to move as many places possible during her 2 weeks stay. I will travel country side in UK in June. I want to see that country and want to meet local people away from cities. Perhaps 2 weeks in UK.

Sounds good to me Shyam!!

I never do like these guys talking about 24 bit A/D ....... us experienced engineers know that the noise floor makes anything above 18 bits very suspicious.... Okay for resolution (short term) but accuracy?!!!

It does make me laugh when I get into a discussion about analogue versus digital and these software guys go on about 24 bits conversion etc.... I've usually found out that its the sales guys who make a song and dance of the number of bits their A/D can resolve, the engineers know better.....

John.

Dear John

This ICL7135 was made robust design and it also takes care of 50/60Hz filter using proper sampling frequency crystal. Charge storage capacitor need to be good and the board very dry, dust free near to those pins else its reading gets affected. Perhaps 4-samples per second is Ok for me to keep an eye on change of reading.

I think an OEM board may be a very good idea. Can you talk to some junior engineers to look into it at your place. In India we do not have many ROHS PCB manufacturers yet. They are still doing in old way and don't care what others say. If I can make this DVM board for say US$20 with parts then I can put it in most of my application. I am using 3-1/2 digit right now. I need to display 15kV as 15.000kV then I can see 1V change.

I have seen some 5-1/2 digit multimeters giving only 0.1% accuracy. Their reading are bull-shit. I no longer trust them for digits. I do not go with precision. You are very much right. engineers know better, what kind of information they have to rely on.

Delta-Sigma are not all that bad. We earlier used 1-bit VCO is same way. Only filter design is different. I am scared of their small size on PCB. I prefer DIP for designs. It allows me to change IC easily. SMDs are bit difficult to work on designs.

IBM-PCs have done a lot of harm to engineering development. Now people know only net, music, video, games etc and lost touch of hard work with analog parts that was once a hreat thing to experience and is still so for me. I work with those transistors, dides, JFETs, NPO caps, MFR, Low noise cables, shielded PCBs, Lots of Aluminum in Box, Closing all possible entry of UFO EMI. I am working on <1nA earth leakage power supplies. Do you think that is possible. We can discuss it else where.

Dear John,

I happened to read this email of yours. It convinced me that still there are people who know very well about ADCs, bits & Bytes !

I have been designing Analaog and mixed signal systems for high performance applications. Many times I come across this demand for 22 to 24 bit ADC from my customers. At times, it becomes very difficult for me to explain the real requirment and pitfalls.

It makes me happy to read such practical views from esteemed designers like you.

Warm Regards,

Gurmeet Singh

CEO,

Global Electronics,

Hyderabad, India

email: g.singh@vsnl.net

Dear Gurmeet

While you have replied to the comments by John, I will like to point out that there are real applications where 20-bit ADCs are in use. One such system I have seen at Mirage Aircraft Engine Testers. These boards were Burr Brown MIL-Grade ADCs are placed in temperature control chamber. ADCs also use isolated power supply, isolated data for least interference. I have no idea of their real accuracy, but can say that they were designed for slow sampling with lots of care.

While accuracy is lot more questionable, we also care for some stable precision, which may be re-calibrated or fitted for better predicted accuracy.

The Wilkinson ADC technology was very interesting one and always produced much better results. It relied on accurate voltage sampling, constant current discharge and a reliable zero voltage level comparator. 14-bit was maximum that I could get from Nuclear Data USA. These were costing few thousands of dollars and were packed in Single Width NIM box. These were for pulse as well as for DC voltage sampling.

The analog world is for those who think that it is immense pleasure to get one extra bit stable in the display. It is not an easy job. Then we do not do easy job. No hard core electronics engineer ever does any easy job.

Accurate reliable off-the-shelf LED indicators and controllers ship for $35-$100 in quantities. Why reconstruct Dodge?

Manufacturing cost of the DPM is only US$10 and sale value at US$20 comes very good. Most of the stock is non ROHS and we want it 100% ROHS. Hence, fresh is fresh and with a fresh look as well. If we do not encourage the new developiers then how will they find themselves in the market. I always look for some one who wants to start at good small circuit and can reach very high in life. I do not believe in big industries, and I am with feelings with small in house engineering anywhere on the earth. It should reach homes in many developing countries is the main idea of injecting reasonable demand. Why should I pay 100$ if some one can do that job for US$20 and can also make profit.

I am to make more engineers and do not want to eliminate them by decreasing the demand. India requires about 1000,000 or one million electronics instruments and circuits in education system alone right now and perhaps this demand will grow for another 30 years. Above that 10000 institutes having on the average 1000 students or 10 million of then require something or the other. Over that we have industrial and research need. I do not think small here and sure nothing less than 10000 numbers.

I have designed circuit based on ICL7135 plus AT89C52.

There was 1 bit error.That I have removed by using simple Digital filter.

bharat

mumbai,India

Dear Bharat

Good. Will to show us the way your board looked and perhaps a picture of it if you can take it using a digicam or scanner? I will like to see and perhaps will like to use the PCB if that is compact. I can redesign it for you if your board shows good temperature stability. I actually want to use these for panel meters to display parameters from my experiments.

Let me know if you wish to share your design details. You can also write to me on my email sst (at) sensorstechnology.com

I will be in Mumbai March 6-9, 2007 in one of the seminar at BARC, Anushaktinagar. If I have your contact numbers then can call you.

hI sir

I am doing a project based on the physical parameter, in which i am using 89s52 and adc 7135cn i am using 2 pins of adc busy and polarity with p3.2 and p3.5 of the microcontroller 89s52, now i am getting the problem to operate the adc and to get the values from it. Please will you help me by sending the code in assembly language for interface the adc with microcontroller

Thank you

Sharath Pandith

Yes I have icl7135 based load indicator for multip. sensors. indicator have seting menu 1 - Baud rate selection 2 - count or table mode selection 3 - reverse reading selection for ultrasonic based level measurement 4 - Print time selection 5 - Relay 1 setpoint selection ( either + or - operation) 6 - Relay 1 hysteresis set 7 - Relay 2 set 8 - Relay 2 hysteresis 10 - Relay 1 set HI/LOW 11 - Relay 2 set HI/LOW 12 - Offset (Indicator will set automatic offset of sensors ) 13 - Display Damping Factor selection (00 for fast Aquisition ) 14 - RS 232 Output selection ( Printer or PC ) 15 - Decimal point selection ( 000000, 00000.0, 0000.00, 000.000, 00.0000) 16 - Calibration factor set ( 40,000 counts) ( + 20,000 to - 20,000 ) 17 - Time totalizer ( rs232 reading out setting in ms for fast xy ploting) 18 - 19 - 20 - 21 - 22 - 4 point linearity setting for non linear sensor 23 - STOR - stor all setting in eeprom we are using this indicator in Automatic filling machine, Shock absorber testing machine, pressure controller, flow controller, Automatic valve controller,Temperature controller, OIT tester, ICF tester, Spring testing machine , Displacement Sensor (LVDT) this indicator have capable to show PEAK-HOLD in both ( +/-) side. You can contect us on 9893008080 Rajendra Singh Precision Instruments GWALIOR www.precision.net.in sales@precision.net.in