Dash Camera Power Supply With Ultra Low "power Off" Consumption (50uA)

 This power source is intended for Dash cameras permanent power supply. Compared to commercial models, my circuit consumes between 1/100th and 1/50th the power of commercial devices in the off state.

I bought the "VIOFO HK3 Hardwire Kit" for the test and saying the truth I don't expect much from it. Then I bought better one and I planed to keep it in my new car. The "MiVue SmartBox lll" is the name, but it is not as smart as it is called. In the "power off mode" when the camera is turned off due to low voltage, it still draws about 3.5 mA from the car battery! In other words, every 12 days it consumes 1 Ah from your car battery. If you add this 3.5 mA to the "normal consumption" of a switched-off "modern car" (which is 2 to 30mA) then, after long-term parking in cold conditions (or if your battery is old) it can cause the car will not start. (BTW the VIOFO HK3 Hardwire Kit takes about 4mA)

 This circuit will help you to save your car battery. My power source for dash cam will takes 1Ah from your battery during 830 days (more then 2 years) not just 12 days! I thing only now it is possible to call the mode "power off mode" even if it is actually still stand by mode.

Notes:

If you do not need the "Power Off" function at the pre-programmed voltage level and you also don't need timer, then you simply do not solder the chip (and its components) to PCB. In such a case the device will work as standard 12V to 5V converter controlled by ACC input. The "Power Off" consumption will stay on 50uA.

I already tested version with possibility to use device in 24V vehicles. The value of R21 is 9.1k, R17 value is 45.3k. It is not so easy to buy E96 decade value but voltage on microcontroller pin must not be higher than 5V! If you will use device in 12V vehicle you can change R17 R21 values as described in schematic diagram.

• I designed the PCB so that I could use the box and cabling from the commercial product SmartBox lll.
• For all those who will implement this project, I have designed a 3D model of the cover, which you can download here. (.stl file)
• The basis is the LM2596M-5.0V converter from China. Yes, you read correctly from China. It has the same designation as the original LM2596. I made device from both, the original and the Chinese copy. There are three differences:
• 1. The original works at a frequency of 150kHz, the Chinese at 56kHz - the original is better here but maximal usable current is also about 1A. It is enough because common dash camera takes usually 0.5 to 0.8A. (Device will work even at 2A consumption without overheating but output voltage on the USB cable end will be about 4V only due to cable small diameter and its relative high resistance.)
• 2. The original in OFF mode takes 170 uA even though according to the catalogue it should have 80 uA! Chinese takes only 50uA! (I tried three pieces)
• 3. I bought ten pieces from China for the price of one original from DigiKey.
• For simplicity and general extension of Arduino, I used the same ATmega328 processor in the design. - We will create our own Arduino from the PCB by burning the bootloader into the processor. For this we will need, for example, an Arduino Uno.
• You will need software Arduino IDE and programmer to program the PCB. Write "Mini USB To FT232 TTL" to ebay or AliExpress to find programmer similar to pictured. The pins on the programmer are in order: DTR, RXI, TXO, VCC, CTS, GND.
• other parts according to the schematics diagram. Used crystal is 3.2 x 2.5 mm in size, for example DigiKey ECS-160-9-33B-CKY-TR. Resistors are 0805 size except R18, R20. Capacitors size is also 0805 except high value capacitors 10uF and above. Switch Digi-Key Part Number 2449-KG04E-ND or similar from China for 1/10 of the price :-). I bought switches here . Inductors I used are: 47uH MGAH1004470M-10 and 6.8uH MGAH06036R8M-10

Notes:

• Schematics is designed in Eagle. Possible to edit if you need. Not possible upload .sch file here so rename file "2023_daschcam5.5.sch.brd" to "2023_daschcam5.5.sch". (erase ".brd" on the end of file name)
• I used low profile small size coils for which I had to create a library in Eagle. You can also use other commonly available coils, but be careful as it is a switching part and for proper operation you must follow the principles described in the LM2595 datasheet. - Lines as short as possible!
• Capacitors should be rated for twice the applied voltage. So C8 470uF/25V for normal cars and 470uF/50V for trucks.

I added this "possibly unnecessary" step for a better understanding of the device's working principle.

The voltage of the car battery goes to the device input "12V". Through the resistor R20, it also reaches the input of the IC LM2596 and keeps it in the off state. The current of the device is determined only by the consumption of the IC. Diode D3 will short-circuits input in case of opposite polarity of input voltage, which melts the protective fuse located on the cable.

If voltage comes also to the "ACC" input, the situation changes. LED1 lights up, transistor T3 opens and the inverting input of the IC is grounded. At the input of the microcontroller D2 comes the voltage from the divider R17/R12 which later on informs the microcontroller (I will write only MC) that the ACC signal is present. Here it is necessary to ensure that the voltage of UD2 does not exceed 5V and this is why the R21 and R17 have different values when using in 12V and 24V vehicles. UD2 = UACC*R21/(R21+R17)

Now the IC starts working at a frequency around 56kHz (the original version of the IC at 150kHz). The voltage of C9 is maintained at 5V by feedback. Here, its shape is still quite saw-toothed looking, so we added a filter element (coil 6.8uH and C12). At C12, the voltage is already almost smooth. We have just produced the voltage needed to power the MC. We will label it VCC.

 After a few seconds, the MC and its program loop will start working. The voltage VCC opens the divider R10/R11 and its voltage leads to input A2 where MC measures its magnitude. To the voltage of the divider R10/R11, we have to add a voltage of approximately 0.2V, which is created by the base current of the transistor T4 and is given by R7 and R11. If we did not use T4, the "Power Off" current of the device would be significantly higher.

MC constantly monitors ACC input. Even after ACC voltage is missing(as we stopped the engine), MC through output D4 keeps T3 open and the device continues to work.

 After disconnecting the ACC, a signal is sent to the P-Pin, the timer is started and the voltage level of the car battery is further monitored. This is of course done by the MC.

After the voltage drops below the set value or after the set time has passed, the D4 output will to 0 level and the T3 transistor will close. This will cause the IC to turn off and of course the MC as well.

There is more that could be written, but I tried to be brief but to the point.

Solder all parts to the chip/processor/mc side only.

It's "in car used" device, so I strongly recommend using a lead solder such as Sn63/Pb37. The new "ecological solders" are not suitable for use in cars, because they cannot handle low temperatures, do not hold well and become porous. (which Falcon Scott was convinced of already in 1911 when he had tanks with heating oil spliced/welded with lead-free tin)

In this step, we actually will create a Arduino compatible board from our our PCB by burning bootloader into the chip. The procedure is on the Internet here: https://docs.arduino.cc/built-in-examples/arduino-isp/ArduinoISP

We only need to correctly connect Arduino Uno pins 10,11,12,13 with our board. The pin order on the board is the same.

In the Adruini IDE, select "Arduino as ISP" from the example, then select "Arduino Pro or Pro Mini" and the correct 5V 16MHz processor. Then set "Arduino as ISP" and burn the bootloader.

After this step we know the chip on the board works - nice, lets continue.

Alternative Option (in case you do not have Arduino Uno) ... buy chip with bootloader or buy Arduino Pro Mini 5V16MHz from China for 2-3 Euros. Desolder chip and solder it on our PBC.

Notes:

• There's no need to solder the wires if you're handy enough, but of course you can solder them if "the devil sits on them"
• There are some other ways to put the code into the chip without a bootloader and without Arduino IDE (e.g. using USBasp), but I think experienced people know how and I don't need to write a hole page about it here.

Download code and open it in Arduino IDE (do not forget to change programmer back to "AVRISP mkll" )

Connect programmer to PC, find correct port in Arduino IDE

Connect programmer an board as on picture.

Upload code. There are two versions of code now. The "standard" version I use in my car the "DashCamV2.81" and new version "DashCam12and24V" for both 12 and 24 Volt vehicles. I can not test device in track because I do not have one. Of course I am open if someone will donate me a truck for tests :-) I used laboratory power supply and 0.5A load to simulation. I tested device and software in 20V to 32V range.

When changing threshold voltage in code (use varriable ''corr'' in code), measure it when device is loaded. Load vill change output votage a bit but it is enought to affect chip's A/D voltage converter in 0.xx range. Exaple: You will sett voltage 12.00V when unloaded, but with camera loaded device the teasured value will be 11.9V. I use 10ohm 25W resistor for tests.

I will describe the code later on but it is well readable I think. Only for the proper functioning of my own camera (Mio MiVue 886), one sequence is inserted in the program, which ensures the correct activation of the recording mode. The sequence is also connected to LED2, so when the device is turned on, LED2 also flashes regardless of the battery voltage.

Note:

There also is no need to solder contacts and actually I do nor recommend do it. It is much easier here comparing the pervious step.

Solder the remaining pats to PCB. - Multi switch is not pictured but solder it too.

- Use "Low ESR" capacitors here, otherwise you risk problems with functionality

- All used ceramic capacitors are for 50V. Yes, on many places it is possible to use 16 or 25V capacitors.

- If you want make the universal device for both 12V and 24V vehicles use exact resistor R17 and R21 to avoid problem with device functionality at low voltage ACC or for not to burn out the MC input pin at high voltage ACC. Second option is to use Zener diode 3.3 to 4.9V instead of R21.

- R19 start value I recommend 10k. For low current LED is possible use value up to 100k. For some old type LED is better to use 2.7k so start with value of 10k ohm it should work.

Note:

I already tested C9 - 330uF/50V which you can use in 24V vehicle. Device will work correctly even data-sheet recommended value is 680uF. C12 I used in that version is 1000uF/16V.

Input side:

GND - GND

12V - permanent connection to car's battery / allays about 12V on pin.

ACC - Voltage 12V only when the car's engine is works / you will find the same marking in your car

Output side:

GND - GND

5V - to 5V USB pin

p-pin - Park pin, used in some models of smart Dash cameras to sett the Parking Mode. / Not necessary for work

• On the input voltage side, connect the fuse boxes to 12V and ACC wire according to the fuse type of your vehicle. (There are 3 different but similarly looking types I know.) The ones you will buy can surely be carefully disassembled and the cable/wire can be connected directly to the connector. Look at the picture how I did it.Such modification then facilitates installation in the vehicle simply because because the cables are softer.

USB cable:

There are two different types of USB Mini cables (see picture) used in the new dash cams and both can be used to connect the dash cam. New Dash cameras have a special type of connector.

• The first one has standard 5 pins in one row only and it is common wide spread cable you can buy on the market. For using in dash cameras it only has 2 wires: +5V and GND. They are usually powered from the cigarette lighter of the car.
• Second one has 3 wires and 10 pins in 2 rows. The third wire is connected in second row. In our Power supply it is marked as "p-pin". This pin allows to switch the camera to "Parking mode". How the Parking mode by itself behaves is set in the camera menu. However, it is generally used to save energy and record events when the vehicle is parked. In my case, it just turns off the screen and the consumption is 40mA less compared to the standard operating mode. This cable is difficult to buy an I used one I bought with "MiVue SmartBox lll". Generally it is not necessary to use p-pin, but because I had cable I designed my device to possibility to use it.

Download and print .stl files (published at step "Supplies"). Cover is designed for 1mm PCB! Use print material suitable for "in car application" as ASA, ABS or similar that can survive warm and cold conditions during all the year. (Another advantage of ASA I used is that you can use acetone for gluing the work or post processing.)

Insert a piece of transparent filament into the hole for the LED or cover it from the inside with transparent adhesive tape

Secure the cable using volcanic mounting tape (I don't know correct English name but tape is like soft as chewing gum and used for waterproofing connectors and similar.). There are openings in both sides of cover for it.

There are 4 switches on the device:

N 1and2 for :Power Off: setting and N 3and4 for timer setting.

You can program switches as you want but I programmed it like this:

switch N | 1 2 | 1 2 | 1 2 | 1 2

..ON.......| 1 1 | 0 1 | 1 0 | 0 0

..............|12.6V | 12.4V| 12.2V|12.0V

.....or......|25.2V | 24.8V| 24.4V|24.0V when device will detect 24V vehicle.

switch N | 3 4 | 3 4 | 3 4 | 3 4

....ON.... | 1 1 | 0 1 | 1 0 | 0 0

.............|OFF | 6h | 12h | 24h

Note: When timer is sett to OFF the device will to "Power off mode" immediately when ACC is missing.

There are two LED:

• The green one, LED1 is on when ACC is connected and device is always ON.Regardless of battery voltage there is 5V on the output.
• The red one, LED2 is on when voltage falls below the set value 12V;12.2V;12.4V or 12.6V. It means: If ACC is OFF and LED2 is ON than the device will to "Power OFF" 120 second after ACC went off.

Timer:

• When ACC is OFF (you park your car) and there is enough power on cars battery (voltage is above the set value) device will to "Power Off" mode after the set time.(6, 12 or 24 hours)
• timer OFF means "Power Off" mode directly after the ACC is OF.

I installed my device in my 2022 Subaru Forester (see picture). Study your car's fuse box in the manual to find out where to connect the 12V and ACC cable..

If you find a grammatical error in the text, write to me and I will correct it. English is not my native language.

Note: As usually due to order my PCB where 5pcs is minimum amount I still have one PCB board I can share. If there are more people who would like to make the project, I can order more PCBs from China.

Here is the "Simplified version" without timer and without battery voltage measurement. It is actually DC/DC 12V to 5V converter driven by ACC input. Dash camera will be powered when the car engine is ON.

I forget to test on oscilloscope the version I have already installed in my car. Here is output signal from "24V vehicle" prototype. Difference is: C8 is 333uF/50V, C9 is 1000uF/16V. Input voltage on test is 13.8V and then 27.6V.

The result of 15 mV Pk-Pk ripple for 12V cars is more than good for such a simple device with only a few components. Value 57mV for 24V is also acceptable i think. I tested the SmartBox lll also, at the same conditions 13.8V input and 0.5A loaded. Here the commercial product is slightly better, about 12 mV vs 8 mV ripple or Pk-Pk 14.83 vs 12.33 mV, but it does not affect the operation of the dash camera, so it is actually an irrelevant value. Value in 100mV range can be relevant in sensitive device but I think even 0.5V ripple will ordinary dash camera accept.

You can use higher inductance and capacitance on output filter. For example 10uH instead of 6.8uH but do not forget coil maximal current limitation and increasing of its resistance. C12 limitation is the size and low ESR. The lower the ESR of the capacitor, the more willing it hold its voltage. Ceramic capacitors have a low ESR and are also suitable for higher frequencies filter, but they do not have sufficient capacity.

There is also possibility to use a bit better value of R10/R11and R7 for more precision work. To add ceramic capacitor parallel to C9 is also a good idea, but then will be device almost perfect and what will I improve then in next version? :-)