You are correct I am in the land of crazy date conventions. I often use 20211126 style because I like to sort things but I am in a minority.
Does anyone know the part number for this kind of enclosure?
A drawing showing the mounting holes might help for designing a PCB.
Cosmin,
Can you recommend enclosures use in the pool industry?
While I have no professional experience I know there are enclosures rated for exposure to the environment and I have read the phrase “wash down” which I think implies spraying with a water hose and perhaps even a pressure washer. IP66 NEMA might be it.
There are also compression fittings to go around cables. Again I do not know the industry to know how to find them.
Please advise so we can help you better.
The enclosure must be IP65 min., but can also be an DIN rail enclosure no matter the IP grade, wich can be mouted in an IP65 bigger box with din rail. At the beggining I didn’t know how big/small the PCB will be so I had to wait and see before I can choose an enclosure.
I will choose the enclosure and I will post drawings and dimmension.
Thank you, guys!
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From my point off view, anyone who has a better idea the the original, can make modifications as long they will lead to a better PCB. You don"t have the stick to the oroginal “design” if you find a better position for a component or a better component as a replacement.
For ex.: I can’t find any THT 80k resisistor so I plan on adding another resistor in serial, like 33k+47k
I haven’t thought so far, I think it’s because of my lack of professional knowledge in electronics … but if you can, and want to, you can make additions or changes to the PCB. This module is intended to monitor and report PH, ORP, PRESSURE and FLOW to a smart home central control unit. The module and the central unit communicate wirelessly through 868 mhz. The central unit also controls wirelessly some actuators that start and stop the pumps. So no mains connected to the board itself.
Maybe these infos help.
Where from this value comes? Are you sure you can’t use standard 82k value?
Why THT. When SMD began to be available for us we started to use them (about 1990). There is no problem to hand solder 0603.
I understand by the relay outputs. I’m used to have wide tracks connected to relay contacts. I double them - the same track at top and bottom (appropriate schematic to avoid crossing these tracks).
Seeing only PCBs I assume you have at the beginning the isolated DC/DC converter. Such converters frequently generate so high common noise that they need to be shorted (input to output) by appropriate capacitor to be in accordance with EMC rules. What datasheet says about it?
Many years ago we were asked if we can improve the device that its manufacturer had continuous problems with them. He had about 50 of them installed and got lot of calls to service them - disconnecting/connecting 12V supply wires helped. Their diagnose was: devices overheat and freeze. When I sow the PCB having 0 protection elements and with 1-wire touch-button socket connected directly to microprocessor pin I told them: The sequence is opposite - microcontroller gets latch-up (because of ESD from touch-button) and then consumes as much current as possible so regulator get hot and its thermal protection limits the current. So the regulator structure is kept at about 120°C and no wonder the housing of the device gets warm.
Your PCB is at that stage now - 0 protection elements. For each wire connected to device you should consider what kind of interference you can expect at it (ESD, Burst, Surge) and how to protect your circuits against them. It depends what is there connected, if that has separate supply and how long is the connection. Right software (ignoring for example short state changes made by ESD) is also a part of protection.
Remember that it happens that lightning strikes somewhere near the building with your devices.
Some time ago I posted here links to (in my opinion) very good papers about that:
See also few posts later in that thread other links I posted.
From what I understood from the guy who designed the whole thing, any other value except 80k will alter the readings of the pressure sensor…
Regarding what you said about protecting the circuits, I don’t have the knowledge to make those improvents… you are asking me to run before I learn to walk.
Any modifications or suggestions are more the welcome.
Regards,
Cosmin
There is a sarcastic saying: Measure with a micrometer, mark it with chalk and cut it with an axe. I guess your schematic is somewhere in this discussion…but anyway digits “80” are not a standard rating.
5% resistor values generally follow the E24 table and 1% resistors follow the E96 table. There are some exceptions. Go to this link and scroll down to see the standard values.
If you think you want “exactly” 80K you should probably choose 1% resistors (pretty widely available) and you could put 2 resistors in series. You could use 78.7K in series with 1.3K. Two in series allows easier fine tweaking. There is nothing generally wrong with putting resistors in series; I often do it for the purpose of flexibility or trying to hit the center of my design tolerance. Of course two resistors require more space and more $ than one.
I know what you are saying. As I said, I will go with 2 in seriesm 33+47k.
If it really needs dialed in that tightly, and I doubt it does, use a trimmer pot in series with a slightly lower resistance than 80K.
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https://www.digikey.com/en/products/detail/vishay-dale/RN65C8002BB14/3342595
https://www.digikey.com/en/products/detail/vishay-dale/CMF5580K000BHEB/3634417
I guess this is a long discussion…diminishing returns. As some others on this forum, I have been engineering for many years. Elaborating on my earlier comment:
Although I have some doubts as to the need for 80K ohms (and not 79K or 81K), I will assume you need 80K ohms.
Your 33K and 47K resistors are probably 5% tolerance. This means that your 80K total could be off by as much as 4K ohms (so you could have something from 76K to 84K) although these days it is very unlikely to be that bad. (45 years ago we were using 5% carbon composition resistors and many samples measured much worse than that.) But my point is that you seem to want a precise value. Given that you should go with a more accurate resistor and a more stable resistor. You probably do not want the value drifting significantly with time or temperature. For that purpose you probably ought to use 1% tolerance (or better) metal film for these resistors. If you do not, then it is a little more like you are cutting with an axe after measuring with a micrometer.
I do not contradict you, because I do not have such advanced knowledge of electronics and that is why I went on what “others thought”, but as I said I am more than open to suggestions and improvements.
I already had resistors 33k and 47k, so that’s why I said I would use those. But, I understood what you said and I will order others.
That sounds good. Using parts that you have is one of the first things to do. Certainly true when the alternative is spending your own money to buy parts. Among the parts that I have are a stash of “5% tolerance” 82 ohm 0.5 watt carbon composition resistors. When I grab one and measure it, it will probably measure outside of the 5% the range between 77.9 to 86.1 ohms.
But carbon composition resistors are not so common these days and carbon film seem to be much more accurate. Metal film is more accurate than carbon film.
I’d use the “vacuo/visuo” approach or “suck it and see”, or, the long version: “try the resistors you have and if that doesn’t give the required results, upgrade to metal film”.
If you are getting a PCB made, as @BobZ has demonstrated elsewhere, make provision for at least the two resistors in series, maybe three. A spare pair of pads can always be replaced with a link if not needed.
If the reading directly draws the display then right, but if it goes through software you can correct the reading according to resistor used. In such case the exact resistor value is less important then its stability over time and temperature. But if you will be buying precision (like 0.1%) resistor then you can buy 80k.
The question is: what is the accuracy of sensor. If it is 5% then using 0.1% resistor makes little sense.
Some thoughts when I looked at the project:
In short, the measurement takes the following route:
- sensor converts pressure to analog signal, presumably the range about 0,675 to 4,5V is used here.
- voltage divider formed by R2 and R3 reduce the analog voltage range to about maximum 3,3V, which is the maximum voltage the AD converter in the 1284 can handle.
- the AD converter reference voltage is 3,3V from the AVCC pin according to the software
- the AD converter is read in the software ( uint16_t readPressure() ), calculations performed to convert the AD reading to display value, and written to display / returned.
The 3,3V reference voltage has, according to the datasheet of the AMS1117-3.3, an accuracy of about 1,5% at 25C, or 3% over the full temperature range of the chip. Using 1% metal film resistors in the voltage divider would make sense, as you would then not significantly add to the uncertainty of the measured value (which could be the case with 5% resistors).
You can easily compensate for a different voltage divider (for example R3 = 82k) by adding a compensation factor to the calculation of float _p = in the readPressure() function.
(For example 82k would give the compensation factor 302/300 or 1,006666…)
Hope it made some sense…
The point is we are sort of talking out loud to one another explaining as we go why more complexity needs to be added for EMC (aka electro magnetic combability) or as Piort wrote: (ESD, Burst, Surge)
Reliability does not happen by accident and you can not count on luck.
This appears to be in reference to R3 near J11.
What connects at J11? ?
Not just what is a Drucksensor? What is the exact manufacturer name and exact part number and better yet a link to it and it’s specification.
Then we can look to see and understand what it is doing and what value of resistor may work.
The resistors R3 and R2 form a voltage divider and I must assume that PA5 is configured as an ADC measuring an analog voltage the Drucksensor provides. This resistive divider is rather high impedance and I would suggest a capacitor to ground, ie in parallel with R2. The value should be to limit the frequency of signals (energy bandwidth) to something with a time constant LONGER than the time between samples of the PA5.
The impedance at PA5 is R2 in paralle with R3 or about 58K. For a one second time constant C must be 1/58K or about 5200 uF. For 1mS time constant C would be 5.2uF
Anyone looked at the software to understand the sampling time?
Pressure sensor 1.2MPa.
| Working Voltage | DC 5.0V |
|---|---|
| Output Voltage | DC 0.5-4.5 V |
| Sensor material | Carbon steel alloy |
| Working Current | ≤10 mA |
| Working Pressure Range | 0-1.2 MPa |
| The Biggest Pressure | 2.4 MPa |
| Cable length | 19cm |
| Destroy Pressure | 3.0 MPa |
| Working TEMP. Range | 0-85℃ |
| Storage Temperature Range | 0-100℃ |
| Measuring Error | ±1.5 %FSO |
| Temperature Range Error: | ±3.5 %FSO |
| Response Time | ≤2.0 ms |
| Cycle Life | 500,000 pcs |
| Application | non-corrosive gas liquid measurement |