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Embedded project needs devices which can work continuously at +125 degree C

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From LM2595 datasheet page no. 25

for fixed voltages of 12V (Vin max 30V) and 3.3V (Vin max 40V) with Iout = 1A I found inductor values as 150uH (1.2A type) and 68uH (1.2A type)

Are these okay ?

- - - Updated - - -

From LM2595 datasheet page no. 25

for fixed voltages of 12V (Vin max 30V) and 3.3V (Vin max 40V) with Iout = 1A I found inductor values as 150uH (1.2A type) and 68uH (1.2A type)

Are these okay ?

Edit:

I searched a lot but could not find 2-Way 5.08 mm or 2.54 mm Pitch Terminal blocks with max operating temperature + 125 or +130 degree C. Can anybody provide links for them ?
 

I am unable to find WROOM-02U that works at +125 deg C and hence we are thinking about putting ESP8266EX (which can operate at +125 deg C) on the main PCB itself and using an external antenna.

If we do like this then do we need to put SPI flash ? As our mikroC PRO PIC program is very small for sending not more than 100 bytes (String Packet) through UART interface. Do we actually need the 1 MB/2MB/4MB SPI flash ?

We have found +125 deg C operating 26 MHz Crystal and also Taoglas external antenna. We want to know what changes we have to do to the WROOM-02U circuit and its RF circuit to be able to use the Taoglas external antenna.

Can we use one of these antennas with WROOM-02U or it modified RF circuit to get 75 meters range indoors with few walls ?

https://www.mouser.in/ProductDetail...BTKBKvsBmlIvfvst9g9R42oKddTOQonJ99xbKMfIfrg==

https://www.mouser.in/ProductDetail/Taoglas/GW260111?qs=sGAEpiMZZMuBTKBKvsBmlKeUqF0pln9Z5XwivYb1C34=

https://www.mouser.in/ProductDetail...BTKBKvsBmlIvfvst9g9R4ku6N8cdy0DIHs/h77uGxtg==
 


ESP8266-01 modules, the postage stamp size ones with internal antenna will reach 75m easily unless there is something shielding the signal. They can be programmed to work as serial to WiFi bridges and there is lots of software out there for them, most of it free to use. For example the Arduino IDE will compile 'C' code for all the ESP8266 and ESP32 modules and it can upload code into them. ESP8266 have an analog input but on some modules it isn't brought out to an accessible pin or pad on the board.

Please note that 125C is the TOTAL temperature of the ambient and internally generated heat, check you do not exceed it in in operational use. I would still recommend you move all the electronics out of the heat and only run the thermocouples inside the furnace. It would remove all the need for high temperature parts, and a high temperature antenna (the short ones in your links will melt!). Also consider that if this furnace has a metal casing, signals will not penetrate it anyway. You already have a cooler region at the heatsink so I would move the electronics there.

Brian.
 


@d123

I need PCB mount type terminal blocks.
 

We found the 2-Way and 3-Way 5.08 mm Pitch, OT +125 deg C type terminal blocks (MI-252 (35/45)).

Find the attached final schematic for the Power Supply. Is there anything I have to change in it ?
 

Attachments

  • TMS-PS-NCN-Pv1.4.PDF
    36.5 KB · Views: 160

You probably don't need the potentiometers, the values are predictable so you should be able to use fixed resistors.
I note you have no over-current protection on the battery charging regulator. Under normal circumstances it would be a good idea to prevent the current becoming excessive but I doubt the Peltier will provide enough current to do any damage anyway.

Note that a safer and maybe cheaper way to protect the voltage measuring points is to remove the 3V3 Zener diodes and instead wire a small (BAT85 for example) Schottky signal diode from the ADC input to VDD. It will conduct and protect the ADC input if the voltage rises above VDD. The action is far more abrupt than the gradual clipping action of a Zener diode.

Brian.
 

@ betwixt

No, I need the trimmers.

Client will use either 4x or 2x batteries and so charging voltages will be either 16.8V or 8.4V from U1. Client will also use either 12V 350mA or 5V 350mA BLDC fan for Peltier cooling and hence I need either 12V or 5V from U2. U3 will provide fixed 3.3V for controller and WiFi.

Okay, I will look for BAT85 equivalent SMD component to do that.

Any other changes needed ?
 
Last edited:

Trimmers are relatively expensive and require manual adjustment using a DVM to monitor the voltage. If it is necessary to cater for both batteries and both fans, it would be cheaper to use one fixed feedback resistor and parallel it with a second fixed resistor and a link.

BAT54 is available in SMD in four versions, the plain BAT54 is a single diode, BAT54A is two diodes with a common anode, BAT54C has two diodes with common cathode and BAT54S has two diodes in series anode to cathode. If you use the BAT54C you can combine your monitoring points protection in a single package. All are SOT23.

Brian.
 

@ betwixt

Okay. Will look at BAT54C.
 

Hi,

mind that BAT54 will have a lot of leakage current at 125°C.

Klaus
 
The power supply circuit is finalised.

Now I have a new question and it is related to ESP8266EX circuit for the same project.

We couldn't find WROOM-02U module which works at +125 deg C and so we are putting ESP8266EX circuit (WROOM-02U) on the main PCB itself and we will be using an external Vertical mount Taoglas Antenna.

In this WROOM-02U datasheet page no. 13/19 (13 of 19) it shows Crystal at 26 MHz +/- 10ppm.

https://download.mikroe.com/documents/datasheets/0c-esp-wroom-02-datasheet-en.pdf

I want to know for what does +/- 10 ppm applies. Is it for tolerance of crystal or Frequency Stability.

Can we use the below Crystal oscillator for it at +125 deg C ?

https://www.mouser.in/ProductDetail...6bBr9Q9abMK2mGYOCsJXY%2bWeR8wmZ8zIZcqH9qUeg==

Edit:

- - - Updated - - -

We are putting the complete WROOM-02U equivalent circuit on PCB and out enclosure is SS (stainless steel) type. So, do will still have to put shielding to ESP8266EX circuit on main PCB as done in WROOM-02U module ? If yes, which suitable shield can we use ?

Edit2:

In this datasheet

https://download.mikroe.com/documents/datasheets/0c-esp-wroom-02-datasheet-en.pdf

Schematics section

WROOM-02U schematic

What should be the tolerances of

L3 (4.3 nH),
C4 (should be L4) 2.4nH
L1 (2.0pF) (Should be C1)
L2 (2.4pF) (Should be C2)
 
Last edited:

Being practical, I would first try some pre-assembled ESP8266 boards at high temperature. Yes, that crystal will work but the chances are one very similar is already mounted on a pre-built module. You would save yourself an enormous amount of development time because the layout is very critical. You would essentially be building a duplicate of an inexpensive part at a much higher price.

Remember also that the ESP8266 alone is of no use unless you code for it in assembly language and keep the firmware very small. The reason most modules also contain a flash ROM is to allow enough storage for things like the ethernet routines, stack and buffers. On pre-built modules the firmware foundations are already present and you can simply call the routines as needed, all the hard work is done for you.

I would be cautious about using a steel shield over the device, they actually run quite hot if continuously transmitting and given your high background temperature I wouldn't advise you to restrict air flow around it.

Those component tolerances should be as tight as possible, they are the antenna matching section and anything that causes an impedance mismatch will reduce the range. As I have said before, I get ranges of more than 75m from bare modules with on-board PCB antennas without any problems. On the modules here, all those components and the crystal together occupy less board area than the IC itself.

Brian.
 
@betwixt

We can't use the pre-built WROOM-02U module as the other associated components like Crystal Oscillator and SPI flash used on that module have operating temperatures (OT) +85 deg C.

Why do I have to code ESP8266EX in assembly ? Explain more. I am using Arduino IDE to write code for it. We are providing a header to on the board to Program the ESP8266EX using TTL2USB adapter.

Tolerance for the Inductors can be 10% and for the Capacitors 5% ?

I should get 75 meters range with few walls.

If I want to get say 85 meters range with few walls then what changes I have to make to the RF antenna section components ? That is what value Inductor and Capacitors I have to use and how to calculate them ?

Also can I use this SPI Flash for the ES8266EX circuit ? It has OT +125 deg C. Is it compatible ?

https://www.mouser.in/ProductDetail...=sGAEpiMZZMuIiYGg9i1FDKGMsfXvViTR4QjgQtYAWuw=


This antenna can use be used for ESP8266EX ?

https://www.mouser.in/ProductDetail/Taoglas/GW260111?qs=sGAEpiMZZMuBTKBKvsBmlKeUqF0pln9Z5XwivYb1C34=

- - - Updated - - -

Sorry wrong antenna link was posted.

Here are out antenna selections. Which one can we use ?

https://www.mouser.in/ProductDetail...BTKBKvsBmlIvfvst9g9R42oKddTOQonJ99xbKMfIfrg==

https://www.mouser.in/ProductDetail...BTKBKvsBmlIvfvst9g9R4ku6N8cdy0DIHs/h77uGxtg==
 
Last edited:

So, What kind of problems with Thermocouple please clarify.
 

@ Aliciamoore

There are no problems with thermocouples. We are using 8x K-type thermocouples to measure furnace temperatures and 1x DS18B20 to measure device temperature and all One-Wire devices (Max31850 and DS18B20).

Did I mention that we have issues using K-type thermocouple ?

In my previous post I have asked if the SPI Flash I mentioned can be used with ESP8266EX.
 

I'm not sure about the flash, you would have to look closely at the ESP8266 data sheet to see if the timing and page layout is compatible. The one on my ESP8266-01 boards is branded "cFeon" with part number "Q80B-104HIP" which is 8Mbits rather than 4Mbits in the device you queried. Bear in mind it contains the OS as well as any program you write for it yourself.

Brian.
 
I would be cautious about using a steel shield over the device, they actually run quite hot if continuously transmitting and given your high background temperature I wouldn't advise you to restrict air flow around it.
Click to expand...

Device wakes up from sleep and then reads the thermocouples and transmits the data and then goes to sleep and repeats it according to the set delay. Delay is in HH:MM format and min delay is 1 minute and max delay is 99 hours and 56 minutes.
 


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