Valden: Heat Pump Controller v1.x

The Valden Heat Pump controller is a platform to precisely control heat pumps. Controller can be easily used for newly designed heat pumps (HPs), including series, as repair controller or as control system for experiments with refrigeration equipment.

!!!GENERATE TOC HERE!!!

Specs

• 12V 0.5A DC power supply,
• 230V output
• up to 12 T sensors, -55..+125 °C range,
• 4 relays: Compressor, Hot CP or Air Fan, Cold CP or Air Fan, Crankcase Heater
• 2 inputs: Hot and cold side refrigerant over/under pressure NC sensors
• 6 pin EEV connection: 4 * coils + 2 * 12V
• control via remote display or local Serial (UART 5V)
• automatically turns on/of system when heating required
• takes care of system components, built-in protections: cold start, overheat, short-term power loss, power overload, ground loop freeze and compressor protection against liquid.
  
  

Refrigeration schemes supported

• Heat Pump (HP) with Electronic Expansion Valve (EEV)
• HP with capillary tube,
• EEV only controller
  
  

Installations supported

• Indoor: a house or technical building with a more or less stable temperature
• Outdoor: harsh climatic conditions taken into account and tested down to minus 32°C
  
  

Changelog and history

• 2018: PCB prototype, first real installation,
• 2019: 2-layer PCB, through-hole components, integrated buttons and display,
• 2019: controller redesigned taking into account development and operating experience,2-layer PCB, SMD
• 2019-2021: installations, development, tests, revisions, redisigns
• 06 Feb 2021: product is technically complete and ready for customers to use. Documentation and release stage.

Get your own copy and PCB assembly

• download the PCB gerber file, {-_Gerber.zip-}
• find in Google, where to order a printed circuit board (keywords: order pcb gerber), place an order,
• order electronic components, see BOM (Bill Of Materials) list, {- _PCB_BOM.html-}
• solder electronic components {- assembly instructions here-}

Firmware upload

The process is the same as for others Arduinos

• connect USB-> UART converter
• start Arduino IDE
• open the firmware file
• select board and MCU in the Tools menu (hint: we are using 328p, 16Mhz, 5V)
• press the "Upload" button in the interface and "Reset" on the Arduino

For arduinos with old bootloader you need to update it. (Tools-> Burn Bootloader).
For successful compilation, you must have "SoftwareSerial", "OneWire" and "DallasTemperature" installed (see Tools -> Manage Libraries).
As a first try it's enough to simply upload firmware without any tunings. Think of it as of commercial closed-source controller, where you cannot change internal options.

Self-tests

QA tests are available to test the assembled board.
Self-test helps you check relays, indicators, speaker and temperature sensors.
To run a self-tests

• uncomment this 3 defines in source code header

//#define SELFTEST_RELAYS_LEDS_SPEAKER    //speaker and relays QA test, uncomment to enable
//#define SELFTEST_EEV                    //EEV QA test, uncomment to enable
//#define SELFTEST_T_SENSORS              //temperature sensors QA test, uncomment to enable

• upload firmware
• connect 12V power supply
  

Video {- demostration "How self-tests works":-} To check EEV, you can use a stepper motor as shown in the video. If you are testing a real EEV, it should be closed after the first "beep" and partially opened after the second "beep".
To check temperature sensors connectors prepare one array of sensors. Connect it to all sensors connectors one-by-one and check results in a serial console.
{-Photo: PCB with connected arrays of sensors (I have enough sensors, so all 3 arrays are connected except Ts2 and Treg) -}
{-Screenshot: serial console with temperature readings: -}

Wiring and installation

Wiring is very simple despite the many connections:
Phases (1st wire in electrical cables):

• connect the "power inlet" wire to one of the "phase" connectors
• and connect the second "phase" connector to the AC input of the 12V power supply
• connect the "Compressor" relay output to the Compressor input
• connect the relay output "Hot CP" to the input of the Hot Circulation Pump (pump of the water floor heating system or the fan input of the indoor unit if you are using an air system)
• connect the relay output "Cold CP" to the input of the Cold Circulation Pump (ground loop pump for geothermal systems or the inlet of the outdoor unit air fan if you are using an air system)
• when using a compressor heater: connect the "Crankcase heater" output to the heater cable input (highly recommended for outdoor installation and year-round use) Neutral (2nd cable in electrical cables):
• connect all the second wires to the "neutral" connectors on the board

{-Photo of HV connections-}

Crimp and connect low-voltage connectors:

• SCT013 sensor (the only low-voltage device in the circuit with interchangeable contacts), connect and install on the phase inlet wire
• RS485 through a wire of the desired length to the remote control display (if used, another control method is a local computer with a USB-UART converter, you may like it for the first time). Note that A is connected to A in the display, B to B and GND to GND
• you can power the display from a 12V controller, the board has 12V and GND secondary pins
• EEV to EEV connector
• T sensors to T sensors connectors
• connect the outputs of the pressure sensors: 1st wires together to the right pin, 2nd cold side wire to the left terminal, 2nd hot side wire to the middle terminal; use the dummy when pressure sensors are not in use.

You may prefer to solder the wires over using connectors. But in this case, it will be more difficult to disassemble the system if you want to change something. The choice is yours.
{-Photo: power wire + SCT013-}
{-Photo: T sensors with abbreviations and full names-}
{-Photo: RS485 and 12V power for display-}
{-Photo: all together-}
{-Photo: ? a crankcase heater looks like ? -}

Starting up the heat pump system for the first time and charging refrigerant

This is not a hard part, but if you don't have experience it will take time.
You have performed a pressure test and vacuumated your system. It's time to charge.
Let's say you don't know how to calculate the amount of refrigerant in a newly built system:

• charge a small amount (for example 300 g) of refrigerant
• start the heat pump
• at this moment the suction temperature (according to the suction pressure on the pressure gauge) will be about -20 ...- 40 ° C
• for single-component refrigerants: slightly open the valve of the HVAC gauge manifold to start adding refrigerant through the gas phase on the cold side,
• for multi-component refrigerants: turn over the refrigerant cylinder, VERY SLIGHTLY open the HVAC manifold valve to start adding a VERY LITTLE amount of refrigerant through the liquid phase
• carry out charging until the suction temperature (according to the suction pressure on the manometer) is ~ 10 ... 15 ° C lower than the temperature of the heat source (example: the temperature at the inlet of the mixture of water and antifreeze from the closed ground loop is + 8 ° C, so the suction temperature should be -2 ..- 7), then close the manifold valve,
• wait for the system to heat the target to a more or less stable temperature, add refrigerant while temperature increases (and suction decreases)
• stop if you are sure that the heating process is now proceeding very slowly
• check the discharge pressure: it should not be too high compared to the temperature from the discharge sensor (Tbc) of the hot side.
• Carry out the final charge when the system is stable and the heat pump stops when the set point is reached (normal stop), this may take 12 hours or more, and now the target difference between the suction pressure temperature and the temperature from the T sensor should be 3 ... 6 ° C,

This algo is good and safe both the first time and as a starting point. As you gain experience, you will get yours much easier and faster. {-Also try "manual EEV mode" during charging process.-} {-?manifold photos with comments?-}

Control and usage: remote control unit

{-There are 2 ways to control heat pump-} qwer

Control and usage: serial console

{-desc 2-} qwer

Diagnostic and status messages

LastStopCause messages. Why system was stopped
P.WtMax:WATTS Protective stop, overcurrent, double check your system, MAX_WATTS and POWERON_HIGHTIME options
E.Tci, E.Tco, E.Tbe, E.Tae, E.Ts1, E.Ts2, E.Tcrc, E.Treg, E.Tac, E.Tbc, E.Tho, E.Thi Sensor lost, check wiring. Refer to "T sensors abbreviations"
E.PresCold Cold side pressure too low, check refrigerant charge and pressure sensors
E.PresHot Hot side pressure too high, check refrigerant charge and pressure sensors

LastStartMessage messages. what event system is waiting for starting work
StCntd:seconds startup countdown, short-term power loss protection #HotPrp:seconds hot side pump is on, waiting for T stabilisation countdown see HOTCIRCLE_CHECK_PREPARE option #HotSlp:seconds sleepeng, last cycle temperature was > setpoint, waiting for next startup, see HOTCIRCLE_START_EVERY option #HPSlp:seconds" + String( (mincycle_poweroff -(unsigned long)(millis_now - millis_last_heatpump_on))/1000 );

#Tho>Max
#Thi>Max
#CaseCold
#CaseHot
#Thi>Setp.
#Ts1>Setp.
#Tae<RefMin
#Tbe<RefMin
#Tbc>Max
#Tci<ColdMin
#Tco<ColdMin

#CWPpStart coldside start, preparing system to start compressor
#CWPp:" + String( (COLDCIRCLE_PREPARE
HP_Started

Normal_stop

HWP_ON

((heatpump_state == 1) && (hotside_circle_state == 0) ) || ((_1st_start_sleeped == 0 )

(millis_now - millis_last_hotWP_on) > HOTCIRCLE_START_EVERY) ) { //process START_EVERY for hot side millis_last_hotWP_off = millis_now; hotside_circle_state = 1; //PrintSS(F("HWP ON by startevery")); lastStartMsgTxt = F("HWP_ON_by_ev");

deffered_stop_hotcircle) || millis_last_heatpump_on == 0) { //deffered stop aftret heat pump stop and correct processing of 1st start, 1st_start sleeped flag not used - there's another logic /* //useful for tank heater with Ts1 as setpont control and large intermediate water reservoir if ( (ThoE == 1 && Tho < (Ts1 + cT_hotcircle_delta_min)) || (ThiE == 1 && Thi < (Ts1 + cT_hotcircle_delta_min)) ) { PrintSS(F("Hot CP OFF 1")); millis_last_hotWP_on = millis_now; hotside_circle_state = 0; } else { PrintSS(F("Hot CP OFF 2")); millis_last_hotWP_on = millis_now; hotside_circle_state = 0; } */ if ( (unsigned long)(millis_now - millis_last_hotWP_off) > HOTCIRCLE_STOP_AFTER) { //and START_EVERY processing #ifdef SETPOINT_THI if ( Thi > T_setpoint ) { #endif #ifdef SETPOINT_TS1 if ( Ts1 > T_setpoint ) { #endif //PrintSS(F("HWP OFF")); lastStartMsgTxt = F("HWP_OFF"); Tci < cT_cold_min) && (coldside_circle_state == 0) ) { //PrintSS(F("CWP ON by ColdMin")); lastStartMsgTxt = F("CWP_ON_CoMin");

cT_hot_max) {heatpump_state = 0; lastStopCauseTxt = F("P.Tho"); cT_hot_max) {heatpump_state = 0; lastStopCauseTxt = F("P.Thi"); cT_crc_max) {heatpump_state = 0; lastStopCauseTxt = F("P.Tcrc") cT_coldref_min) {heatpump_state = 0; lastStopCauseTxt = F("P.Tae"); cT_before_evap_work_min) {heatpump_state = 0; lastStopCauseTxt = F("P.Tbe"); cT_coldref_min) {heatpump_state = 0; lastStopCauseTxt = F("P.Tsuc") cT_before_condenser_max) {heatpump_state = 0; lastStopCauseTxt = F("P.Tbc"); cT_cold_min) {heatpump_state = 0; lastStopCauseTxt = F("P.Tci"); cT_cold_min) {heatpump_state = 0; lastStopCauseTxt = F("P.Tco");

cT_workingOK_crc_min ) ) { //errorcode = ERR_HEATPUMP; millis_last_heatpump_on = millis_now; heatpump_state = 0; LSCint = LSCint_protective; lastStopCauseTxt = F("P.W.TcrcMIN"); c_workingOK_wattage_min ) ) { //errorcode = ERR_WATTAGE; millis_last_heatpump_on = millis_now; heatpump_state = 0; LSCint = LSCint_protective; lastStopCauseTxt = F("P.W.wattMIN"); "E.PressHot"); _LO) { "E.PressCold");

"Err: "); PrintSS_SaI(errorcode);

Additional messages
OK:E.T.Sens. Sensor restored
OK:Pr.Cold Cold side pressure restored
OK:Pr.Hot Hot side pressure restored

Firmware options and fine tunings

QA tests, uncomment to enable

//#define SELFTEST_RELAYS_LEDS_SPEAKER	//speaker and relays QA test, uncomment to enable
//#define SELFTEST_EEV			//EEV QA test, uncomment to enable
//#define SELFTEST_T_SENSORS		//temperature sensors QA test, uncomment to enable

Communication protocol with external world, choose one

//#define RS485_JSON	1	//json, external systems integration
//#define RS485_HUMAN	2	//RS485 is used in the same way as the local console, warning: Use only if 2 devices (server and this controller) are connected to the same RS485 line
#define RS485_MODBUS	3	//default, Modbus via RS485, connection to the display (both sensor or 1602, see https://gitlab.com/valden/) or connection to any other MODBUS application or device 

System type, comment both if HP with EEV

//#define	EEV_ONLY	//Valden controller as EEV controller: NO target T sensor. No relays. Oly EEV. Sensors required: Tae, Tbe, current sensor. Additional T sensors can be used but not required.
//#define	NO_EEV		//capillary tube or TXV, EEV not used

Which sensor is used to check setpoint, uncomment one of options

#define SETPOINT_THI	//"warm floor" scheme: "hot in" (Thi) temperature used as setpoint
//#define SETPOINT_TS1	//"swimming pool" or "water tank heater" scheme: "sensor 1" (Ts1) is used as setpoint and located somewhere in water tank

Some more options

#define HUMAN_AUTOINFO	30000	//print stats to console, every milliseconds
#define WATCHDOG		//disable for older bootloaders

Next sections: advanced options Temperature sensors used in a system, comment to disable

#define T_cold_in;		//cold side (heat source) inlet sensor
#define T_cold_out;		//cold side outlet sensor
#define T_before_evaporator;	//"before" and "after evaporator" sensors are required to control EEV, both "EEV_ONLY" and "full" schemes 
#define T_after_evaporator;	//"before" and "after evaporator" sensors are required to control EEV, both "EEV_ONLY" and "full" schemes 
#ifdef SETPOINT_TS1
	#define T_sensor_1;	//T values from the additional sensor S1 are used as a "setpoint" in "pool" or "water tank heater" schemes 
#endif
//#define T_sensor_2;		//additional sensor, any source, for example: outdoor temperature, in-case temperature, and so on
#define T_crc;			//if defined: enables crankcase T sensor and crankcase heater on relay 4
//#define T_regenerator;	//an additional sensor, the regenerator temperature sensor (inlet or outlet or housing) is used only to obtain a temperature data if necessary 
#define T_afrer_condenser;	//after condenser (and before valve)
#define T_before_condenser;	//before condenser (discharge)
#define T_hot_out;		//hot side outlet
//in full scheme Hot IN required! optional in "EEV_ONLY" scheme (see "EEV_ONLY" option), 
#define T_hot_in;		//hot side inlet

Temperature limits

#define MAGIC		0x66;	//change this value if you want to rewrite the T setpoint in EEPROM 
#define	T_SETPOINT	26.0;	//This is a predefind target temperature value (start temperature). EEPROM-saved. The value can be changed using 1. Console 2. Changing the "setpoint" on a display 3. Changing this value AND changing "magic number"
#define T_SETPOINT_MAX	48.0;	//maximum "setpoint" temperature that an ordinary user can set
#define T_SETPOINT_MIN	10.0;	//min. "setpoint" temperature that an ordinary user can set, lower values are not recommended until antifreeze fluids at hot side are used.
#define T_CRANKCASE_MIN		8.0;	//compressor (crankcase) min. temperature, HP will not start if T lower
#define T_CRANKCASE_MAX		110.0;	//compressor (crankcase) max. temperature, overheating protection, HP will stop if T higher
#define T_CRANKCASE_HEAT_THRESHOLD 16.0;//crankcase heater threshold: heater will be powered on if T lower
#define T_WORKINGOK_CRANKCASE_MIN  25.0;//compressor temperature: additional check. HP will stop if T is lower than this value after 5 minutes of work. Do not set the value too large to ensure normal operation after long pauses. 
#define T_BEFORE_CONDENSER_MAX	108.0;	//discharge MAX, system stops if discharge higher
#define T_COLDREF_MIN 		-14.0;	//suction min., HP stops if T lower, cold side (glycol) loop freeze protection and compressor protection against liquid 
#define T_BEFORE_EVAP_WORK_MIN 	-25.5;	//!!!before evaporator (after valve) min. T; can be very low for a few minutes after startup, ex: capillary tube in some conditions; and for all systems: after long shut-off, lack of reagent, 1st starts, and many others
#define T_COLD_MIN 		-15.5;	//cold side (glycol) loop freeze protection: HP stops if inlet or outlet temperature lower
#define T_HOT_MAX 		50.0;	//hot loop: HP stops if hot side inlet or outlet temperature higher than this threshold

Watts, cycles times (milliseconds)

#define MAX_WATTS	1000.0 + 70.0 + 80.0	//power limit, watt, HP stops in case of exceeding, example: compressor: ~1000 + hot CP 70 + cold CP 80
#define POWERON_PAUSE     	300000    //after power on: 			wait 5 minutes  before the start of HP (protected from power faults) 
#define MINCYCLE_POWEROFF 	600000    //after a normal compressor stop: 	10 minutes pause 	(max 99999 seconds) 
#define MINCYCLE_POWERON  	3600000  //after compressor start: 		minimum compressor operation time, i.e. work time is not less than this value (or more, depending on the setpoint temperature) 60 minutes = 3.6 KK 120mins = 5.4 kK.
#define POWERON_HIGHTIME	7000	//after compressor start: 		defines time when power consumption can be 3 times greater than normal, 7 sec. by default
#define COLDCIRCLE_PREPARE	90000	//before compressor start:		power on cold CP and wait 90 sec; if false start: CP will off twise this time; and (hotcircle_stop_after - this_value) must be > hotcircle_check_prepare or HP will go sleep cycle instead of start
#define DEFFERED_STOP_HOTCIRCLE	1200000	//after compressor stop:		wait 20 minutes, if no need to start compressor: stop hot WP; value must be > 0
#define HOTCIRCLE_START_EVERY	2400000	//while pauses:				pump on "hot side"  starts every 40 minutes (by default) (max 9999 seconds) to circulate water and get exact temperature reading , option used if "warm floor" installation (Thi as setpoint)...
#define HOTCIRCLE_CHECK_PREPARE	300000	//while pauses:				...and wait temperature stabilisation 5 minutes (by default), after that do setpoint checks...
#define HOTCIRCLE_STOP_AFTER	(HOTCIRCLE_CHECK_PREPARE + COLDCIRCLE_PREPARE + 30000)		//...and then stop after few minutes of circulating, if temperature is high and no need to start compressor; value must be check_prepare + coldcircle_prepare + 30 seconds (or more)

EEV options If you are using capillary tube or TXV: simply skip next section Depending on how many milliseconds are allocated per step, the speed of automatic tuning will change. Remember that you'll see refrigeration system reaction on every step not immediately, but after few minutes, sometimes after tens of minutes.

#define EEV_MAXPULSES		250	//max steps, 250 is tested for sanhua 1.3

//steps tuning: mulliseconds per fast and slow (precise) steps
#define EEV_PULSE_FCLOSE_MILLIS	20	//(20 tube evaporator)		fast closing, closing on danger				(milliseconds per step)
#define EEV_PULSE_CLOSE_MILLIS	60000	//(50000 tube evaporator)	accurate closing while the compressor works 		(milliseconds per step)
#define EEV_PULSE_WOPEN_MILLIS	20	//(20 tube evaporator)		standby (waiting) pos. set				(milliseconds per step)
#define EEV_PULSE_FOPEN_MILLIS	1400	//(1300 tube evaporator)	fast opening, fast search 				(milliseconds per step)
#define EEV_PULSE_OPEN_MILLIS	70000	//(60000 tube evaporator)	accurate opening while the compressor works		(milliseconds per step)
#define EEV_STOP_HOLD		500	//0.1..1sec for Sanhua		hold time						(milliseconds per step)
#define EEV_CLOSEEVERY		86400000	//86400000: EEV will be closed (zero calibration) every 24 hours, executed while HP is NOT working	(milliseconds per cycle)

//positions
#define EEV_CLOSE_ADD_PULSES	8	//read below, additional steps after zero position while full closing 
#define EEV_OPEN_AFTER_CLOSE	45	//0 - set the zero position, then add EEV_CLOSE_ADD_PULSES (zero insurance, read EEV guides for this value) and stop, EEV will be in zero position. 
					//N - set the zero position, than add EEV_CLOSE_ADD_PULSES, than open EEV on EEV_OPEN_AFTER_CLOSE pulses
					//i.e. it's a "waiting position" while HP not working, value must be <= MINWORKPOS
#define EEV_MINWORKPOS		50	//position will be not less during normal work, open EEV to this position after compressor start

//temperatures
#define EEV_PRECISE_START	7.0	//(8.6 tube evaporator) 	precise tuning threshold: 		make slower pulses if (real_diff-target_diff) less than this value. Used for fine auto-tuning
#define EEV_EMERG_DIFF		1.7	//(2.5 tube evaporator) 	liquid at suction threshold:		if dangerous condition occured:  real_diff =< (target_diff - EEV_EMERG_DIFF)  then EEV will be closed to min. work position //Ex: EEV_EMERG_DIFF = 2.0, target diff 5.0, if real_diff =< (5.0 - 2.0) then EEV will be closed to EEV_MINWORKPOS
#define EEV_HYSTERESIS		0.5	//(0.6 tube evaporator) 	hysteresis, to stop fine tuning:	must be less than EEV_PRECISE_START, ex: target difference = 4.0, hysteresis = 0.3, no EEV pulses will be done while real difference in range 4.0..4.3 
#define EEV_TARGET_TEMP_DIFF	3.6	//(3.6 tube evaporator) 	target difference between Before Evaporator and After Evaporator, the head of whole algorithm

//additional options
#define EEV_REOPENLAST		1	//1 = reopen to last position on compressor start, useful for ordinary schemes with everyday working cycles, 0 = not
#define EEV_REOPENMINTIME	40000	//after system start: min. delay between "min. work pos." (must be > 0 in this case and > waiting position) set and reopening start
//#define EEV_MANUAL			//comment to disable, manual set of EEV position via console; warning: this option will stop all EEV auto-activities, including zero position find procedure; so this option not recommended: switching auto/manual mode from console after startup is a better way

//do not use next option untill you're not really need it
//#define EEV_DEBUG				//debug, usefull during system fine tuning, works both with local serial and RS485_HUMAN

Communication addresses

const char devID  = 0x45;	//used only if JSON communication, does not matter for modbus and Valden display https://github.com/OpenHP/
const char hostID = 0x30;	//used only if JSON communication, not used for modbus

Last option

#define MAX_SEQUENTIAL_ERRORS 	15 		//max cycles to wait auto-clean error, ex: T sensor appears, stop compressor after counter exceeded (millis_cycle * MAX_SEQUENTIAL_ERRORS)

Diagnostic and troubleshooting

{-describe messages-} qwer

T sensors abbreviations

Abbreviations used in the documentation and firmware

Main sensors:

Abbr.	Full name
Tae	after evaporator
Tbe	before evaporator
Tci	cold side "input"
Tco	cold side "output"
Tbc	before condenser
Tac	after condenser
Thi	hot side "input"
Tho	hot side "output"
Tcrc	crankcase (compressor itself)

Additional sensor used in "swiming pool heater" or "water tank heater" schemes:

Abbr.	Full name
Ts1	additional sensor1

Additional sensors, disabled and not used by default:

Abbr.	Full name
Treg	regenerator temperature
Ts2	additional sensor2

Hints

For more information about Heat Pumps look at Wikipedia about HP.
If you are interested in questions like "how refrigeration systems works" read Patrick Kotzaoglanian books.
If you want more technical details, sophisticated scmemes, "how EEV can be driven by temperature" diagrams, etc. refer to vendors manuals (you can find a lot in Alfa Laval brochures, Danfoss guides, and so on).
For refrigerants and oils types comparison see wiki.

Personal experience

Note that the SCT013 sensor and the current monitoring scheme cannot be used for accurate measurements and accurate COP calculations. Use wattmeter for accurate power measurements.
Measuring the temperature of a warm floor with sensor at one point is a bad idea - it's better to deal with temperature of the "hot in" water coming from all over the floor, as implemented in firmware.
The weather-dependent (both outdoor and indoor temperature dependent) system does not work fine for 30-150 m2 buildings. The system turns out to be difficult and works bad due to unpredictable ventilation. And also due to the unpredictability of heat emitted in the house by other sources.
I tried the scheme with a flooded evaporator in 2019 and found it extremely problematic, then refused to use it.
Deep regeneration schemes are useful only for some refrigerants and only in certain temperature ranges. I also tried deep regeneration, I was convinced that the theory coincides with the practice and then also refused this idea.
In general, it is possible by complicating the refrigeration scheme to win somewhere 1%, somewhere 3%, but all this leads to significant time and money costs, compared to not very much profit.
Summary: If you want experiments - Experiment. Want reliably and quickly - make system simple.

License

GPLv3.

This product is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

Author

gonzho АТ web.de (c) 2018-2021