Level and distance gauge with alarm function [140209-I]

This project achieves a measuring instrument with the following functions:

This project achieves a measuring instrument with the following functions:

Measurement of liquid levels
Level monitoring function with relay output and LED alarm indicator
Programmable min/max alarm levels
Storage of min/max calibration values for 10 different containers or tanks
Distance measurement
Intuitive menu guidance via LCD display

Many of us are aware of this problem: The lawn mower requires gasoline and we don't know how much petrol in the petrol tank is left. The shake test provides only vague results. Or we want to find out the level of an oil tank or rainwater cistern. Another practical example: We fill a big container with the garden hose with water, but we don’t want to observe this process until the container is full. Here the water supply can be interrupted by a solenoid valve automatically when the desired level is reached. Or you would like to simply gauge the distance between two objects. Read the attached documents and you can realize a low-cost instrument with a high utility value.

Revision 1
English and german documentation corrected

Revision 1.1
English and german documentation expanded

Revision 1.2
Schematic figure for calibrating empty level corrected in english and german documentation

Revision 1.3
Some indefinite descriptions and translation mistakes corrected

Revision 1.4
Bug in menu navigation resolved - new software version added
English and german documentation expanded

Revision 1.5
English and german documentation corrected

Revision 1.6
Component change: Regulator LT 1086 CT-5 replaced with type LM2940CT-5 because of lower dropout voltage.
English and german documentation corrected

Revision 1.7
Code optimization and comments added

Revision 1.8
Code optimization and comments added

Revision 1.9
Hardware change: 2.2 KOhm (R4) resistor added to pulldown the ECHO-port.
Some US-modules need this resistor to work properly.
Circuit diagram, english and german documentation corrected

Revision 2.0
Weblink added to english and german documentation

Revision 2.1
Code correction: If no echo signal should be received an error message will be displayed now.

Revision 2.2
Code correction: If no echo signal should be received the software may hang in a loop when using the module DYP-ME007. To prevent this problem a watchdog logic is implemented now. Does not occur when using module HC-SR04, because this module has a hardware timeout.

Revision 2.3
Code correction: Logic for mode 'Level Watchdog' corrected - was defect since last update. ASCII-value for displaying level as bargraph changed for using lcd MC41605A6WK.

Revision 2.4
Code correction: Software timeout handling for US-modules without hardware timeout corrected.

Project Elements

Circuit diagram (JPG, 94.81 KB)

LevelDistanceGauge.zip (ZIP)

Program code

Level and distance gauge.zip (ZIP)

English documentation

Pegel- und Distanzmessgerät.zip (ZIP)

Deutsche Dokumentation

Discussie (5 opmerking(en))

ClemensValens 10 jaar geleden

Hi,

Do you think it is wise to drive the relay directly from the MCU? I don't know which kind of relay you use, but typical 5V ones I usually encounter start at some 40mA. The ATmega8 datasheet lists this value as the absolute maximum value for an I/O pin. Furthermore, at 40mA the I/O pin output voltage drops to 4V. The hold current for the relay will be lower, still it feels a bit risky. Since you don't clearly specify the relay, people may use anything they have lying around. What does it cost to add a transistor to drive the relay? It would make the circuit more robust.

Regards,
Clemens

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JoergT 9 jaar geleden

Hi Marc, I thank you for your comment. If the level meter is used for a tank with flammable content, the relay for safety reasons should not be used for driving a pump or other equipment with high power consumption to avoid sparking. The ultrasound technology itself is no problem. Commercial units operate with the same technology. The following link leads to a research report, which examined this topic . Conclusion of this report is, that no accidents were detected, which were triggered by ultrasound. http://www.bgrci.de/fileadmin/BGRCI/Downloads/DL_Praevention/Explosionsschutzportal/Wissen/Forschungsbericht_Z%C3%BCndwirksamkeit_Ultraschall.pdf Kind regards, Joerg

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giant 9 jaar geleden

Hi Guys, It's a nice project but take care. Never use this solution onto a fuel tank. It is not explosion proof and therefor very dangerous to operate in the neighborhood of any inflammable fluids and or gases. Kind regards, Marc

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JoergT 10 jaar geleden

Hi, I studied different 5 volt relay data sheets and found out that the minimal required voltage is between 3 and 3.5 volt. So, we should not expect problems when using a 5 volt relay. Best regards, Joerg

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JoergT 10 jaar geleden

Hi, I think, if we give a hint which relay is to use, the ATMega8 driving port will not be damaged. The following relay type is configured for 4.5V: AXICOM V23079-A1011-B301 http://www.pollin.de/shop/dt/NDk0OTU2OTk-/Bauelemente_Bauteile/Mechanische_Bauelemente/Relais_Zugmagnete/Relais_AXICOM_V23079_A1011_B301.html This relay is configured for 4.5V and has a resistance of 145Ω. When the port output voltage is between 4V and 4.5V we have a current consumption between 27mA and 31mA. The resistance of the used relay should not be lower than 130Ω. The problem is: The layout has to be changed. But, if you think that this a critical part, I would agree to use an addtional driver transistor. How to do this you can see here: http://home.arcor.de/joergt59/Elektor/RelayDriver/RelayDriver.jpg Best regards, Joerg

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Lucky 10 jaar geleden

Some minor software issues to be solved, hardware works OK.

The LCD we chose -Midas MC41605A6WK-SPTLY, to be more precise- has an on-board resistor for its LED backlight. This means the backlight can be directly connected to +5V without additional current limiting, so we could have omitted the anode resistor (R3) on the PCB. However, if another brand or type of LCD is used this resistor can be handy, or the connections of R3 can be used to add an ON/OFF switch to the backlight to save energy when the circuit is battery powered. But of course R3 can also be replaced by a jumper wire when our type of LCD is used.

schematic-4.jpg (205kb)
pcb-top.jpg (63kb)
pcb-bottom.jpg (63kb)

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Lucky 10 jaar geleden

Nope, this resistor is on the PCB (disguised as R1 ;-)). You use 'R' also as reference for the contrast potentiometer, I changed that to the Elektor-style 'P', so there's one 'R' less in my schematics...

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JoergT 10 jaar geleden

Resistor R4 is missing in the current PBC and should be added to guarantee that the echo port is pulled down to LOW if no echo should be received after 200ms. In the schematic and documentation this resistor is listed since revision 1.9.

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Lucky 10 jaar geleden

Not too difficult to solder and the hardware isn't too complicated, so I didn't expect much issues. However, I was unpleasently surprised by the LCD I ordered (Powertip PC1604LRU-AWB-H), which appeared to need a negative voltage on the contrast pin (VO on pin 3) to get readable text on the display. For the time being this was solved with the good-old diode trick (schematic) to get one end of the contrast potmeter at -0.7V. The result is not really encouraging, but I can still use this LCD before I get a more modern LCD in stead.

Negative contrast voltage on LCD modules was quite common 'in the old days', but I hadn't seen one for years!

diode-trick.jpg (67kb)

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JoergT 10 jaar geleden

Hi Luc, Answering your questions during my holidays is no problem, it's like reading the newspaper at breakfast ;-) While I have developed the software, I have also thought about storing user-defined offset values for the housing width and the outside temperature. Here you can read the description of the original documentation you can find as project attachment: >> Was the first launch successful the basic settings can be made now. For this purpose turn off the power again. Now hold the Return key pressed while turning on the device. After releasing the Return key, the user is prompted for the width of the box. This value is important to correct the distance measurement, because the measurement starts from the rear of the box. So you can for example easily measure the distance from wall to wall. The value for the box width can changed in 5 mm steps using the + and - buttons. After confirming the input with Return you are prompted for the divisor value. This value is used for a measurement result correction at air temperatures below 15 ° C or above 25 ° C, if you want to reach a high accuracy. Note that the higher the temperature the greater must be the value of the divisor. To get good results make a reference measurement in front of a wall in 2 m distance for example. After confirming the divisor value by pressing Return again the actual program starts. If you can live with an inaccuracy of about 5% in the temperature range from 0 ° C to 40 ° C, you can skip this menu item by pressing Return. The values for box width and divisor are retained even after changing the battery and may be re-configured using the above-described process. << You see, the two offset values are not static in the software and can be changed dynamically by the user. Hope, I could help you with this information. Best regards, Joerg

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Lucky 10 jaar geleden

Hi Joerg, You were not supposed to reply before next week ;-) I won't stop you if you want to squeeze the watchdog in too, I was just trying to make it easier for you. Anyway, it can still be mentioned for people who want to extend the functionality of this project. I knew that there was be a good reason for the distance offset! My mind too much set to the liquid level measurement I guess. Still it would be nice if the user can set the reference point manually without changing the firmware, but that will be too much to ask if you want to stick to the ATmega8. Recalibrating a tank is easier than I thought... Best regards, Luc

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JoergT 10 jaar geleden

Hi Luc, To take the next higher ATMega type is a good suggestion, but nevertheless I'll try to shrink the code for implementing a watchdog function :-) When you are using the distance mode, the distance will be measured from the back of the box to the target object. Why should I do this? Well, in this mode I want to measure the distance from wall to wall for example. So I have to calculate from the back of the box. That's the way commercial distance gauges are working also. The constant Box_width_default is used if the user didn't store a user defined offset value for the box width in the EEPROM variable Saved_box_width. How you can change this value is described in the documentation. The default value is set to 7.5 cm. I hope my explanation was good enough to understand the reason for this procedure. It's no problem to recalibrate a used tank number. Just call the calibration menu for the selected tank and execute the calibration again. Best regards, Joerg

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Lucky 10 jaar geleden

Hi Joerg, The new LCD certainly is an improvement, no negative voltage needed for the contrast. If flash memory is a limiting factor for further development or improvement, I would suggest to use an ATmega168, which has twice the amount of program memory. The software runs on this microcontroller and it’s pin compatible with the ATmega8. It’s just a bit more expensive than the ATmega8, and it will save a lot of time trying to optimize the code size. I noticed that there is an offset of 7.5cm in the distance measurement, which is related to the constant value of Box_width_default added to the measured value in software. I don’t quite get why you are adding this constant, but I’m very sure you have a good reason (preferably with an explanation ). Maybe you can add a routine to set a zero-distance point for this measurement? Is there a procedure to recalibrate, or to clear the min and max settings of a tank? Best regards, Luc

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Lucky 10 jaar geleden

Hi Joerg, Enjoy your holiday first! :-) Best regards, Luc

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JoergT 10 jaar geleden

Hi Luc, That every LCD manufacturer cooks his own soup is really annoying! Changing the software and implementing a watchdog function is a good idea, but not easy to realize because of no more free memory - it is in use to 100%. I read your comment just in my holiday and will be back at the 17th of august. Then I will try to optimize the memory consumption for implementing the additional code. Best regards, Joerg

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Lucky 10 jaar geleden

Hi Joerg, There are many alternatives for the LCD, for now I've ordered the MC41605 (Midas) which should arrive today. Of course the dimensions of the display module are important (we want to fix the LCD to the PCB), and (what's even trickier) the interface connector must fit the footprint on the PCB. The Powertip display has this connector shifted 100mil to the left side compared to the one from Midas, and it seems like every manufacturer has his own standard :-( However, it looks like the prototype is working fine! Some minor things to change though, I made a mistake in the PCB, swapped the Return and Next buttons. Easy to change in software of course, but I prefer to correct it in hardware to prevent confusion in firmware versions. One thing (so far) that should be corrected in the software: Trigger_out = On 'Create 10us pulse to trigger US module Waitus 10 Trigger_out = Off Time_value = 0 Timer1 = 0 Do 'Waiting for receiving US signal (echo) Loop Until Echo_in = 1 This works fine under normal conditions, but if -for some reason- the US pulse is not sent or the echo not received, the software will never exit the loop. A time out plus corresponding error message would be more elegant. Best regards, Luc

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JoergT 10 jaar geleden

Hi Luc, the LCD you ordered is only nearly the same I used. Here you can read the data of the panel LCD TC1604A-05: http://www.pollin.de/shop/downloads/D120689D.PDF I'm astonished that there are such differences. Using a negative voltage is not state of the art, I think also. At Farnell alternatives are available. What do you think about FDCC1604A-FLYYBW-51LK ? http://www.farnell.com/datasheets/653684.pdf This company sells 13 different types of LCD 16x4 displays. No easy choice... Kind regards, Joerg

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Lucky 10 jaar geleden

Hi Joerg,

I've started working on the project, schematic design in Altium Designer is nearly finished, PCB design will begin soon.

Some comments on the schematics though, I hope you don't mind. First I'd rather use the LM2940T than the -CT version (temperature range to -40 instead of 0 degrees). I also added a 47u capacitor to the output (see datasheet), and some decoupling for the LCD supply.

Maybe I just overlooked, but I didn't find details on the relay, can you please help?

Best regards,

Luc

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JoergT 10 jaar geleden

Hi Luc, I ordered the box from Pollin: http://www.pollin.de/shop/dt/Njk5OTM1OTk-/Bauelemente_Bauteile/Gehaeuse/Kunststoffgehaeuse_021_002_113.html In this shop you can order a very cheap relay: http://www.pollin.de/shop/dt/NDk0OTU2OTk-/Bauelemente_Bauteile/Mechanische_Bauelemente/Relais_Zugmagnete/Relais_AXICOM_V23079_A1011_B301.html It's a 4.5V relay, but I think, that's no problem. If so, you could wire a standard diode in serial connection to the relay and would have a voltage loss of about 500 mV to reach 4.5V. Perhaps you can find these parts in another shop. Best regards, Joerg

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Lucky 10 jaar geleden

Hi Joerg, Thanks, I saw RS-Components recently added these relays to their shop. Voelkner will be okay for our German (and European) readers, but we have customers all over the world and RS will be easier for them. I like the enclosure you used, can you tell me what brand and type it is? Best regards, Luc

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JoergT 10 jaar geleden

Hi Luc, I would advise you the following relay types: http://www.voelkner.de/products/383253/Netzrelais-HF41F-Hongfa-HF41F-005-ZST-5-V-DC-1-Wechsler-Max.-6-A-Max.-30-V-DC-277-V-AC-Max.-1500-VA.html http://www.voelkner.de/products/541729/Miniaturrelais-HJR-4102-Tianbo-Electronics-HJR-4102-L-05VDC-S-Z-5-V-DC-1-Wechsler-Max.-5-A-Max.-60-V.html http://www.voelkner.de/products/37873/Signal-Relais-2u-5V-2A-Ds2y.html Use a relay with a power on and a power off switch. So the user can deside what should happen when the alarm is triggered - turn off or on a pump or other devices. I wish you good luck while realizing the project. If you should have any problems, ask me. I'll try to answer as fast as possible. Best regards, Joerg

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Lucky 11 jaar geleden

Hi Joerg,

I really like this project :-) Did you make a PCB layout or did you take a piece of veroboard to build the circuit?

Regards,

Luc

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Lucky 11 jaar geleden

Hi Joerg, That won't be too difficult, sounds like a good idea :-) Regards, Luc

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JoergT 11 jaar geleden

Hi Luc, I wouldn't say no to this plan ;-) Here an idea I had yesterday: If you realize a PCB an external power supply socket could be added. Then it would be possible to use the gauge for steady-state operation when using the watchdog function. Regards, Joerg

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Lucky 11 jaar geleden

Hi Joerg, Good chance that we will plan the project for publication, we'll design a PCB then ;-) Regards, Luc

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JoergT 11 jaar geleden

Hi Luc, I'm glad that you like this project. But I'm sorry, currently there is no PCB layout available. I took a piece of veroboard to build the circuit. Having a PCB layout would be a good idea. So other users could realize this project without any problems. Regards, Joerg

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