Hartmut Sonnenberg - Freelance Software Developer

Q: Where is Hartmut based?

Hartmut is based in Biberach an der Riß, Germany and can operate in on-site , hybrid , and remote work models.

Q: What languages does Hartmut speak?

Hartmut speaks the following languages: German (Native), English (Intermediate) .

Q: How many years of experience does Hartmut have?

Hartmut has at least 34 years of experience. During this time, Hartmut has worked in at least 2 different roles and for 2 different companies . The average length of individual experience is 1 year and 1 month . Note that Hartmut may not have shared all experience and actually has more experience.

Q: What is Hartmut's latest experience?

Hartmut's most recent position is Freelance Software Developer .

Q: What companies has Hartmut worked for in recent years?

In recent years, Hartmut has worked for Syneco Trading GmbH and Self-employed .

Q: Which industries is Hartmut most experienced in?

Hartmut is most experienced in industries like Manufacturing , Energy , and Healthcare . Hartmut also has some experience in Automotive , Utility Services , Media, and Entertainment and Publishing .

Q: Which business areas is Hartmut most experienced in?

Hartmut is most experienced in business areas like Information Technology (IT) , Product Development , and Business Intelligence . Hartmut also has some experience in Human Resources (HR) , Operations , and Finance .

Q: Which industries has Hartmut worked in recently?

Hartmut has recently worked in industries like Manufacturing , Energy , and Healthcare .

Q: Which business areas has Hartmut worked in recently?

Hartmut has recently worked in business areas like Information Technology (IT) , Product Development , and Business Intelligence .

Recommended expert

Biberach an der Riß, Germany

Experience

Jan 2026 - Dec 2026

1 year

Biberach, Germany

Freelance Software Developer

Replaced conventional database access with REST APIs using HTML (MS Graph, Powerbot) in Excel, Access, and C# applications.
Designed and implemented REST interface integrations in existing Office and .NET solutions.

Jan 2025 - Present

1 year 2 months

Biberach, Germany

Freelance Software Developer

Supported and enhanced the Access VBA application "Reporting Headcount Time Management on SAP basis" developed in 2019 for a globally active mechanical engineering company.
Updated the application for changed corporate structures.
Maintained import, analysis, and reporting functionality for employee and time management data.

Sep 2024 - Dec 2024

4 months

Biberach, Germany

Freelance Software Developer

Supported the Access VBA application "Reporting Headcount Time Management on SAP basis" for a global mechanical engineering company.
Adapted it to updated corporate structures and revised the evaluation logic for headcount and time management metrics.

Jun 2024 - Present

1 year 9 months

Biberach, Germany

Freelance Software Developer

Replaced conventional database access with REST APIs using HTML (MS Graph, Powerbot) in Excel, Access, and C# applications.
Migrated existing Office solutions to modern API-based data integration.

Jan 2024 - Present

2 years 2 months

Biberach, Germany

Freelance Software Developer

Syneco Trading GmbH

Maintained, enhanced, and developed new Excel VBA tools.
Implemented and optimized Oracle 19 database access.
Adapted and extended data access layers (SQL, PL/SQL) in existing reporting and analysis tools.

Oct 2023 - Present

2 years 5 months

Biberach, Germany

Freelance Software Developer

Syneco Trading GmbH

Maintenance, enhancement, and new development of Excel VBA tools.
Implementation and optimization of Oracle 19 database access.
Ongoing expansion of reporting and analysis functions for trading and energy data.

Apr 2023 - Sep 2023

6 months

Biberach, Germany

Freelance Software Developer

Syneco Trading GmbH

Migration of extensive Excel VBA applications from 32-bit to 64-bit.
Adjustment of data access libraries to Oracle 19c.
Extension of database logic using stored procedures to improve performance and functionality.

Jan 2023 - Feb 2023

2 months

Biberach, Germany

Freelance Software Developer

Further development of a time management reporting application based on SAP for a global machine manufacturer (plastic processing machinery producer).
Analysis of employees’ age structure within the time data.
Creation of a health index for each age group based on time management data.

Jun 2022 - Dec 2022

7 months

Biberach, Germany

Freelance Software Developer

New development of a C# and WPF client application (Visual Studio 2022, SQL Server 2019) for medical administrative software.
Design of the database schema, creation of tables, stored procedures, and functions in SQL Server.
Programming of the C#/WPF frontend.
Deployment of the application as a COM DLL according to customer requirements.

Feb 2022 - May 2022

4 months

Biberach, Germany

Freelance Software Developer

Adjustments to updated business and legal requirements of a long-maintained Excel VBA price comparison application for an energy company.
Maintenance of calculation logic and updating of reporting functions.

Feb 2022 - Apr 2022

3 months

Biberach, Germany

Freelance Software Developer

Modifications and further development of a Visual Basic 6 DATEV XML online module.
Continued the development that started in the second half of 2021 for the digital transfer of booking data to DATEV.

Jan 2022 - Jan 2022

1 month

Biberach, Germany

Freelance Software Developer

Provided support for the Access VBA application "Reporting Headcount Time Management on SAP Basis" for a global machine engineering company.
Adapted the application to changed corporate structures.

Sep 2021 - Dec 2021

4 months

Biberach, Germany

Freelance Software Developer

Developed a Visual Basic 6 application for a medium-sized company (automotive) to automatically prepare booking data (incoming and outgoing invoices, cash transactions) from an ERP system (MariaDB).
Transformed the data into DATEV-compatible XML files for online transfer to the DATEV server.
Goal: eliminate manual booking entry by the supporting tax firm.

Jul 2021 - Aug 2021

2 months

Biberach, Germany

Freelance Software Developer

Developed an Excel VBA application for time data capture.
Imported and analyzed employee master data and time data.
Created tabular reports and charts for flexitime balances, overtime, and vacation days.
Generated emails to cost center managers with the relevant reports.

Apr 2021 - Jun 2021

3 months

Biberach, Germany

Freelance Software Developer

Further developed and adapted a VB6-based ERP/CRM system for a medium-sized client.
Maintained and expanded the application using MariaDB as the backend.
Ongoing support with a monthly workload of about 20%.

Jan 2021 - Sep 2021

9 months

Biberach, Germany

Freelance Software Developer

Development and modernization of an Excel VBA analysis tool for medical substance analyses and intolerances.
Revamp of an existing customer information system in Excel VBA with a modern interface (ribbon bar, callback functions).
Refactoring of heavily outdated code (architecture redesign).
Implementation of multilingual support for nutrients, email texts, and other content.
Addition of numerous new features in the analysis and reporting area.

May 2020 - Aug 2020

4 months

Biberach, Germany

Freelance Software Developer

Updates to the database design and stored procedures in MS SQL Server for a water management engineering firm.
Programming and expansion of an Excel VBA application to analyze water management data based on new requirements (continuation of the 2018 project).

Feb 2020 - Dec 2020

11 months

Biberach, Germany

Freelance Software Developer

Further development of an Excel VBA price comparison application for an energy company to evaluate tranche contracts.
Project phases from 02/2020 to 05/2020 and 11/2020 to 12/2020.
Maintenance of the calculation logic and adjustment to market and contract requirements.

Dec 2019 - Aug 2020

9 months

Biberach, Germany

Freelance Software Developer

Support and modifications of an Access VBA gas/electricity pricing application for SMEs (small and medium-sized enterprises) for an energy company.
Further development of a price comparison application for old and new contracts.
Maintenance of user interfaces, calculation logic, and reporting.

Jun 2019 - Feb 2020

9 months

Biberach, Germany

Freelance Software Developer

Development of an Access VBA application "Reporting Headcount Time Management on SAP Basis" for a global machine manufacturer (producer of plastic processing machines).
Import of employee and time management data from SAP into an Access database.
Provision of extensive analysis tools and reports (creation of time data, health rates, personnel development).
Export options for reports to Excel and PDF.

May 2019 - Dec 2019

8 months

Biberach, Germany

Freelance Software Developer

Migrated a screw calculation program from a Visual Basic 6 application to an Excel VBA application for a plastic processing machinery manufacturer.
Converted all class definitions, properties and methods of the original VB6 application into VBA classes.
Ensured functional parity and extensibility in the new environment.

Jan 2019 - Apr 2019

4 months

Biberach, Germany

Freelance Software Developer

Developed an asynchronous backup solution using VB.NET and MSForms.
Controlled MS Robocopy in a BackgroundWorker process for asynchronous execution of copy operations.
Implemented interprocess communication between the user interface and the copy process.
Goal: reliable backup of data files to external drives with status feedback to the user.

Mar 2018 - Sep 2018

7 months

Biberach, Germany

Freelance Software Developer

Developed an Excel VBA analysis tool for the HR department of a plastic processing machinery manufacturer.
Analyzed all employee time data (flexitime, vacation, sick leave).
Replaced an old dBase IV application with a modern Excel-based solution offering improved analysis and usability.

Jan 2018 - Dec 2018

1 year

Biberach, Germany

Freelance Software Developer

Supported and customized an Access VBA pricing application for gas/electricity for SMEs for an energy company.
Enhanced a price comparison tool for old and new contracts in Access and Excel.
Maintained pricing logic, reports, and user interfaces.

Jan 2018 - Dec 2018

1 year

Biberach, Germany

Freelance Software Developer

Designed the database schema and developed the required stored procedures in MS SQL Server for a water management engineering firm.
Programmed an Excel VBA application to store and analyze rainfall and runoff data.
Retrieved measurement data from MS SQL Server through the Excel frontend and visualized it using charts.

Apr 2017 - Feb 2018

11 months

Biberach, Germany

Freelance Software Developer

Adapted a dBase IV application for the HR department of a plastic processing machinery manufacturer.
Updated the table design and developed new features.
Adjusted and extended existing reports.

Jan 2017 - Dec 2017

1 year

Biberach, Germany

Freelance Software Developer

Developed an Excel VBA application for employee goal tracking for a plastic processing machinery manufacturer.
Added functions to export and import data from individual goal achievement files.
Supported the HR department in goal recording and evaluation.

Apr 2002 - Jul 2010

8 years 4 months

Biberach, Germany

Freelance Software Developer

Developed an Excel VBA and Oracle-based price calculation tool for an energy producer to set prices in the electricity market.
Incorporated production costs and load profiles to supply large customers with price information.
Covered the entire business process from offer to signed contract and electricity supply.
Programmed the Excel interface and worked on the data model for the Oracle database.
Implemented stored procedures to capture the business logic.

Mar 1999 - Feb 2001

2 years

Biberach, Germany

Freelance Software Developer

Programmed a booking program for a post-production team with Visual Basic 6 and an Access database backend.
Planned and managed post-production resources (studios, staff) using a graphical user interface.
Supported scheduling to efficiently use rooms and equipment.

Apr 1997 - Nov 1999

2 years 8 months

Biberach, Germany

Freelance Software Developer

Developed Visual Basic 6 DLLs and a Visual Basic frontend application for a reinsurance company.
Implemented a multi-layered architecture with an Oracle database (3-tier model).
Built an ActiveX server frontend and several DLLs in the middle tier on a Windows Server.
Applied object-oriented design within the constraints of Visual Basic 6.

Aug 1996 - Apr 1997

9 months

Biberach, Germany

Freelance Software Developer

Programming a booking program for a recording studio using Visual Basic 6 and an Access database as the backend.
Supporting scheduling by planning studios, sound engineers, and producers.
Graphical planning and blocking or allocating resources for specific production periods.

Jan 1993 - Present

33 years 2 months

Biberach, Germany

Freelance Software Developer Visual Basic, VBA, C# and WPF

Self-employed

Development of custom software for reinsurers, companies in the advertising and film industries (recording studios and post-production companies).
Many years of development work for an energy group, a mechanical engineering company, and an engineering firm for water management in residential areas.
In recent years, additional projects for companies in the automotive and energy sectors, as well as in medical software.
Focus areas: C# and WPF (since 2012), databases (MS Access, MS SQL Server, Oracle, MariaDB), Standard SQL, MS Transact SQL, Visual Basic 5.0/6.0 (since 1995), VBA for Microsoft Office (Excel and Access, since 1994).
Advanced skills: integrating REST APIs into VBA applications including Auth1.0 and Auth2.0, automated email sending via MS Graph sendMail, Oracle PL/SQL, XML, XAML, HTML, CSS, Python.
Good knowledge of the .NET Framework and Windows APIs.
Many years of continuous collaboration with multiple companies, high reliability in scheduling and communication with clients.

Industries Experience

See where this freelancer has spent most of their professional time. Longer bars indicate deeper hands-on experience, while shorter ones reflect targeted or project-based work.

Experienced in Manufacturing (33 years), Energy (33 years), Healthcare (33 years), Automotive (33 years), Utilities (33 years), and Media and Entertainment (33 years).

Manufacturing

Energy

Healthcare

Automotive

Utilities

Media and Entertainment

Business Areas Experience

The graph below provides a cumulative view of the freelancer's experience across multiple business areas, calculated from completed and active engagements. It highlights the areas where the freelancer has most frequently contributed to planning, execution, and delivery of business outcomes.

Experienced in Information Technology (34 years), Product Development (33 years), Business Intelligence (14 years), Human Resources (3 years), Operations (2 years), and Finance (1 year).

Information Technology

Product Development

Business Intelligence

Human Resources

Operations

Finance

Summary

Since 1993, I have been developing custom software for reinsurance companies and businesses in the advertising and film industries, such as recording studios and post-production companies. I have also done long-term, diverse development work for an energy group, a mechanical engineering firm, and a civil engineering office in urban water management.

Clients get a highly experienced, dedicated developer with a quick grasp of things. Meeting realistic deadlines and clear communication with the client are a given for me. Also typical is my long-term collaboration with multiple companies.

Skills

Main Areas

Software Development In C# And Wpf Since 2012
Database Development With Ms Access, Ms Sql Server, Oracle, And Mariadb
Standard Sql, Ms Transact-sql
Software Development In Visual Basic 5.0 And 6.0 Since 1995
Vba Development For Microsoft Office (Excel And Access) Since 1994

Additional Skills

Experience Integrating Rest Apis Into Vba Applications, Including Auth 1.0 And Auth 2.0
Programmed Email Sending Not Via Outlook (Classic) But Using Ms Graph Sendmail
Oracle Pl/sql, Xml, Xaml, Html, Css, Python
Good Knowledge Of The .Net Framework And Windows Apis

Languages

German

Native

English

Intermediate

Profile

Created

February 2026

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Frequently asked questions

Do you have questions? Here you can find further information.

Where is Hartmut based?

Hartmut is based in Biberach an der Riß, Germany and can operate in on-site, hybrid, and remote work models.

What languages does Hartmut speak?

Hartmut speaks the following languages: German (Native), English (Intermediate).

How many years of experience does Hartmut have?

Hartmut has at least 34 years of experience. During this time, Hartmut has worked in at least 2 different roles and for 2 different companies. The average length of individual experience is 1 year and 1 month. Note that Hartmut may not have shared all experience and actually has more experience.

What roles would Hartmut be best suited for?

Based on recent experience, Hartmut would be well-suited for roles such as: Freelance Software Developer, Freelance Software Developer Visual Basic, VBA, C# and WPF.

What is Hartmut's latest experience?

Hartmut's most recent position is Freelance Software Developer.

What companies has Hartmut worked for in recent years?

In recent years, Hartmut has worked for Syneco Trading GmbH and Self-employed.

Which industries is Hartmut most experienced in?

Hartmut is most experienced in industries like Manufacturing, Energy, and Healthcare. Hartmut also has some experience in Automotive, Utility Services, Media, and Entertainment and Publishing.

Which business areas is Hartmut most experienced in?

Hartmut is most experienced in business areas like Information Technology (IT), Product Development, and Business Intelligence. Hartmut also has some experience in Human Resources (HR), Operations, and Finance.

Which industries has Hartmut worked in recently?

Hartmut has recently worked in industries like Manufacturing, Energy, and Healthcare.

Which business areas has Hartmut worked in recently?

Hartmut has recently worked in business areas like Information Technology (IT), Product Development, and Business Intelligence.

What is the availability of Hartmut?

Hartmut will be available part-time from April 2026.

What is the rate of Hartmut?

Hartmut's rate depends on the specific project requirements. Please use the Meet button on the profile to schedule a meeting and discuss the details.