SmaTrig 2.1

HDR-Jack 2 - The improved HDR and interval trigger

This article explains how to build the second improved version of the HDR-Jack. In contrast to the original circuit this version is powered from a lithium coin battery. This results in compatibility with cameras not supported by the first version, because of the focus wire issue. The circuit can be easily embedded in the enclosure of a cable remote controller as shown in the pictures below. The original function of the cable release is preserved.

HDR-Jack 2 top view HDR-Jack 2 open

Modes of operation

The following table lists all functions of the HDR-Jack 2. They are activated by pushing the small "extra" button. Modes 1 to 5 provide different bracketing series and an interval function. Modes 6 to 17 allow the configuration of the trigger.

PressesLong last press
1aHDR uni 2 EV 1-
1bInterval 1yes
2aHDR day 2 EV 2-
2bHDR day 1 EV 2yes
3aHDR night 2 EV 3-
3bHDR night 1 EV 3yes
4a HDR ML uni 2 EV4-
4b HDR ML uni 1 EV4yes
6 set exp. gap to 0.25 s  6-
7 set exp. gap to 0.5 s 7-
8 set exp. gap to 0.75 s8-
9 set exp. gap to 1.25 s9-
10set exp. gap to 2 s10-
11set exp. gap to 3 s11-
12no skip 12-
13skip < 1/60 13-
14skip < 1/8 14-
15shutter only 15-
16focus + shutter 16-
17focus then shutter 17-

Functions 1a) to 4b) can be interrupted by pushing the button once. "Long last press" means that the button is pressed for more than 0.5 second during the last press. Examples:

Mode 1a: _______-______________

Mode 1b: _______-----------____

Mode 2a: _______-__-___________

Mode 2b: _______-__--------____

and so on...

Detailed description of functions

1a) HDR uni 2 EV
This is the all-purpose bracketing series with an EV step of 2. The nominal exposure times are 1/125, 1/30, 1/8, 1/2, 2, 8 and 30 seconds. The shortest time might vary strongly depending on the camera.

1b) Interval mode
The hold time of the button is used as the interval period. The duty cycle is approx. one. Example: Holding the button down for 4 s results in a trigger sequence with 2 s on and 2 s off.

2a) HDR day 2 EV
This is a short bracketing series for daylight conditions with an EV step of 2. The nominal times are 1/200, 1/60, 1/15, 1/4 and 1 second. The shortest time might vary strongly depending on the camera.

2b) HDR day 1 EV
This is a short bracketing series for daylight conditions with an EV step of 1. The nominal times are 1/200, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2 and 1 second. The shortest time might vary strongly depending on the camera.

3a) HDR night 2 EV
This is a short bracketing series for low light conditions with an EV step of 2. The nominal times are 1, 4, 15, 60 and 240 seconds.

3b) HDR night 1 EV
This is a short bracketing series for low light conditions with an EV step of 1. The nominal times are 1, 2, 4, 8, 15, 30, 60, 120 and 240 seconds.

4a) HDR ML uni 2 EV
This is the all-purpose bracketing series with an EV step of 2 and mirror lock-up support. The nominal exposure times are 1/15, 1/4, 1, 4, 15 and 60 seconds.

4b) HDR ML uni 1 EV
This is the all-purpose bracketing series with an EV step of 1 and mirror lock-up support. The nominal exposure times are 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8, 15, 30 and 60 seconds.

This function has been left blank intentionally to avoid unintended change of settings.

6) to 11) Exposure gap settings
Using these functions the time gap between the exposures in the bracketing sequences can be changed. The value is saved permanently in the EEPROM of the microcontroller. This feature has been implemented to optimally exploit the possibilities of the camera in use and keep step with the development. Setting a larger gap gives you possibility to check the histogram in the preview after each exposure so you can abort the bracketing and save time.

12) to 14) Short exposure skip
The minimum bulb exposure time of some camera modells might be longer than the times provided by the HDR-Jack 2. The effects are skipped shots or jumping exposure times. To avoid unnecessary waiting or unusable shots, you can skip the shortest times according to the description in the table. The limiter is also practical if the first shots result in the same exposure level.

15) to 17) Trigger pulse settings
These functions allow to change the way the trigger pulse is generated. Different camera modells behave differently depending on how the trigger signal is applied. DSLRs of the EOS xxxD series and the 1000D show best reproduction of the nominal exposure times when triggered using the shutter wire only. In contrast, the EOS 40D needs always both wires for bulb exposure.

Usage of HDR modes

  • Plug in trigger
  • Set the camera to the manual mode M
  • Set shutter speed to BULB
  • Set aperture
  • Focus on scenery
  • Set camera to manual focus
  • (Enable mirror lock-up if desired)
  • Trigger by pushing the small "extra" button

The interval mode requires no special settings on the camera. It is recommended to use manual focusing especially for dark scenes to avoid missed triggers caused by focus hunting.


The HDR-Jack 2 uses the bulb mode to control the exposure time. This very simple principle avoids complicated protocols and is compatible with many camera types, but also has its limitations. The biggest one concerns the minimum exposure time. To my knowledge, the shortest exposure time observed with a Canon DSLR in bulb mode is about 1/200 s. With other brands this time becomes even longer (measured 1/10 with Nikon D80, 1/8 wit Sony a350, heard of 1/60 with Pentax). Unfortunately it is not possible to control the camera properly at very short times. Older Canon cameras without live-view seem to perform better than newer ones. For live-view types from Canon exposure times shorter than approx. 1/4 s become increasingly instable and might be missed by the camera.
Another limitation concerns the EXIF data generated by DSLRs in bulb mode. Canon limits the precision to seconds, so every exposure under 1 s will result in an EXIF exposure time of 1 s. Sony cameras write 1/10 s for every bulb exposure under 1 s.


Basically all cameras with a cable remote control connector and the bulb exposure option are compatible with the HDR-Jack 2 if the aforementioned limitations are taken into account.
The following table lists optimal settings for different camera types. The data is obtained from own tests or is reported by users. You are welcome to contribute! The exposure gap can be set depending on your preferences. Longer times let you check the exposure.

CameraEx. gap [s]Exp. SkipPulseComment
EOS 350D (XT)1.25noneSShortest exp. approx. 1/180 s
EOS 400D (XTi)1.25noneSShortest exp. approx. 1/180 s
EOS 450D (XSi)1.25< 1/60SShortest exp. approx. 1/60 s
EOS 500D (T1i)1.25< 1/8SShortest exp. approx. 1/2 s
EOS 550D (T2i)1.25< 1/8SShortest exp. approx. 1/4 s
EOS 1000D1.25< 1/60?Shortest exp. approx. 1/60 s
EOS 20D 1.25< 1/60SShortest exp. approx. 1/60 s
EOS 30D 1.25??
EOS 40D 1.25noneF+SShort exp. brighter than nominal value
EOS 50D 0.75??Shortest exp. approx. 1/4 s
EOS 60D 0.75none?Shortest exp. approx. 1/100 s
EOS 5D ???Compatible, no info on short times until now
EOS 5Dmk2?< 1/8xShortest exp. at approx. 1/4-1/8 s, one user reported 1/100 s
EOS 7D ?< 1/60F+SShortest exp. approx. 1/60 s
Pentax K100D SuperCompatible
Nikon D300< 1/8F+SShortest exp. approx. 1/8 s
Nikon D700< 1/8F+SShortest exp. approx. 1/8 s
Nikon D5000< 1/8F+SShortest exp. approx. 1/8 s
Nikon D90< 1/8F then S1/4 s shortest exp. time
Fuji S3 ProF+S1/4 s shortest exp. time
Sony a3501.25< 1/60F+S1/8 s shortest exp. time
Sony a1000.75< 1/60F+S
Lumix GF1?< 1/60F+SShortest exp. approx. 1/30 s, needs adapter circuit
Olympus E-5101.25< 1/60F+SShortest exp. approx. 1/30 s


HDR-Jack 2 gallery

Taken by Feldman, a true HDR enthusiast

HDR-Jack 2 gallery bracketing series

Metro station "Hallesches Tor" in Berlin. The bracketed images were merged using enfuse, own work.

HDR-Jack 2 gallery

Old town in Krakow. Merged using enfuse and stitched with Autopano, own work.

HDR-Jack 2 built by reader

HDR-Jack 2 built by Björn Hövelmann. A socket was used to allow reprogramming of the AVR.

HDR-Jack 2 gallery

HDR-Jack 2 built by Sönke Martens. The button is positioned in the lower end of the cable release body.

HDR-Jack 2 by Felix Kramer

HDR-Jack 2 built by Felix Kramer.

HDR-Jack 2 by Kerstin

HDR-Jack 2 built by Kerstin.

The Circuit

HDR-jack 2 schematics

The circuit consists of just three parts. The ATtiny25 AVR microcontroller, a push-button and a battery. The whole circuit has a current consumption of just 5 uA in active mode and <0.5 uA in stand-by. Assuming an average supply current of 1 uA and a battery capacity of 200 mAh a theoretical life time of 200000 hours can be expected. This is more than 20 years.

Parts and Assembly

The ATtiny25 can be replaced by the ATtiny45 or ATtiny85. The only difference is the flash memory size (and the price). There is also a low voltage version of the controller with a V appended to the name (ATtinyXXV). It is also a very good (or even preferred) choice. The battery should be a 3 volt lithium type or a stack of standard batteries. The 2032 is a good choice because of the large capacity and good availability/price. For the push-button a standard tactile switch can be used. A plunger length of ~3.5 mm is recommended if the switch is mounted as shown in the title picture above.

Software and programming

The code is written in C. Because the controller is permanently connected to the battery, it is essential to keep it in power-down mode most of the time to save battery life. All timing functions are implemented using the watchdog timer running at 128 kHz. The watchdog timer is strongly voltage dependent, but does a good job in the application described here.
After initialisation the uC is put into sleep until the button is pressed. Depending on the number of presses and the duration of the last press, one of the functions described above is executed. Each function ends with a hardware reset carried out by the watchdog.
The configuration functions make use of the EEPROM of the AVR to store the values permanently.

You will need a programmer to transfer the hex and eep file to the microcontroller. There is a big variety of programmers on the market and on DIY web sites. Depending on the features (USB, parallel port, JTAG, debugging functions) the cost ranges between 1 and 100 Euros. I use a home-brew STK200 clone for the parallel port. I you want to buy a programmer, go for a simple and popular (forum support) USB version. The good thing about programmers is that any programmer will program any AVR microcontroller.
If you are not familiar with microcontrollers I strongly recommend to go through one of the beginner tutorials at avrfreaks. German-speaking readers should have a look at

If you have your programmer working, the programming is rather straightforward. It is advisable to change the fused called SUT0 and SUT1 to 'fast rising power' to avoid the current peak after power-on. This is recommended but not necessary for correct operation of the HDR-Jack 2. The clock source is unchanged (8 MHz internal oscillator).
Do not forget to program the EEPROM!

HDR-Jack 2 fuses


hdr-jack2.hex - hex file (FLASH)
hdr-jack2.eep - eep file (EEPROM)
HDR-Jack_2_Bedienungsanleitung.pdf - manual in German

Can you build one for me?

Many people ask me to build the HDR-Jack 2 for them, because they don't have the programming tools or the necessary skills in electronics. So, from time to time I build a few them for others. You can contact me via e-mail (English or German) at



For post-processing of the images I recommend to use enfuse with enfuseGUI. Both programms are free.

Your ideas are welcome. If you want to propose a new function, please use the comment box below.

The author takes no responsibility for any injury or damage resulting from the operation or construction of the device presented here.

First battery-free version of the HDR-Jack
Remote trigger pinout of the Canon EOS 400D
ATtiny25 data sheet
enfuse is a free exposure blending tool for realistic looking results
Windows GUI for enfuse
Qtpfsgui - free HDR software
An interesting paper about exposure fusion, a must for enfuse users

Comments (26)

#26 - Werner - 01/10/2012 - 18:59
HDR-Jack 2
#25 - Mecki - 11/15/2011 - 17:51
#24 - Bastian - 08/12/2011 - 12:23
HDR-Jack Anfrage
#23 - todden - 08/10/2011 - 21:23
HDR-Jack für 5D MK 2
Das Gerät würde mich für die 5D MK 2 sehr interessieren. Was würde es kosten und wie lange müsste ich warten.

Viele Grüße

#22 - Thomas Kreil - 05/11/2011 - 17:23
atmel version
Both versions of the chip can be used. The tiny25 and the tiny25V are ok. The chip is supplied with 3 V from the battery, so the supply voltage is not critical here.

#21 - luk - 05/10/2011 - 11:58
#20 - Heinz Rettig - 01/31/2011 - 14:47
Source code for Program
Greate project.
Would you please publish a source code for the program. I like to port it to PIC microprocessor. I am familiar with it and have the programmer and a compiler.

Thank you in advance.
#19 - David - 01/27/2011 - 01:54
Jede Menge Anfragen von willigen Kaeufern. Wenn ihr eure Email Adresse und Preisvorschlaege hinterlassen wuerdet, dann koennten sich andere Hobbybastler mit euch in Verbindung setzen.
#18 - Marco - 08/07/2010 - 03:02
#17 - Tom - 07/27/2010 - 14:28
#16 - Hartmut - 07/26/2010 - 11:34
#15 - Melo - 06/15/2010 - 11:07
Danke Luk
#14 - Gerhard - 04/12/2010 - 17:49
Source code
#13 - luk - 03/29/2010 - 10:30
#12 - Jo - 03/17/2010 - 20:31
#11 - Friedhelm Wien - 03/03/2010 - 15:47
#10 - Manfred - 02/14/2010 - 00:01
#9 - Heino - 02/06/2010 - 15:00
HdR Jack2
#8 - Rocky Kunkel - 01/11/2010 - 01:50
Interesse an einem HDR JACK 2
#7 - Michael Schoene - 12/13/2009 - 19:36
Anfrage zu HDR-Jack II
#6 - Anonymous - 10/15/2009 - 11:07
Anfrage HDR-Jack II
#5 - Susanne Krofta - 09/11/2009 - 07:03
#4 - Jacques - 08/20/2009 - 11:03
Funktioniert perfekt an EOS 1000D
#3 - Jacques - 08/20/2009 - 11:00
battery grip
Hi Norbert,

many thanks for the feedback on the 20D. I investigated the battery grip bracketing idea recently. I think it should work fine. There is enough space to embed an AVR inside the grip and the power supply is no problem. Take a look on the article "EOS battery grip disassembled" on this site. You'll find there a close-up of the dial wheel and a description how it works.

#2 - luk - 08/17/2009 - 10:55
HDR Jack2 on my Canon EOS 20D works perfect!!!
I use to have a AVR Butterfly to make HDR's in Bulb mode of my 20D.
Now I have have a HDR Jack2 and everything work fine to me!
I need to setup the HDR Jack2 as follows:

Mode 9 (exp gap 1,25 s)
Mode 13 (skip < 1/60)

Additional I set to Mode 15 (shutter only), but I'm not sure if this is necessary...

I think about installing the HDR Jack2 into my battery grip, but in the moment I just think about...

For me everything works PERFECT!!!

Thanks for HDR Jack2
#1 - Anonymous - 08/15/2009 - 09:07
E-mail (Will not appear online)
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