Plans for the alleged 21 July terror attacks were made because mainstream protests against the Iraq war were not working, a court has heard.
Mr Ibrahim said he wanted to "cause panic" but not hurt anybody
Muktar Ibrahim, 29, told Woolwich Crown Court he had made the devices which failed to go off across London's transport network.
He planned to create a "fake explosive" in a demonstration that would cause panic but not hurt anybody, he said.
Six defendants deny conspiracy to murder and to cause explosions.
The men are accused of carrying out an extremist Muslim plot designed to cause chaos in July 2005.
Mr Ibrahim, from Stoke Newington, north London, who wore a pink tie, lilac shirt and dark suit, is the first of the six to appear in the witness box.
He told the court that he and co-defendant Yassin Omar had taken part in several anti-war demonstrations across London against what was happening in Iraq and Afghanistan.
"Seeing non-Muslims protesting and speaking out about the war made me feel as a Muslim that I should do something stronger," said Mr Ibrahim.
He said he became increasingly determined to do something after reading a letter posted on a website from a woman prisoner claiming she was raped by her captors at Abu Ghraib prison in Iraq.
Mr Ibrahim said: "It made me even more determined to take positive action against the injustice that is taking place in Iraq."
The idea for the 21 July attacks came from a discussion with Mr Omar, the court heard.
Mr Ibrahim said: "Omar said something like, 'what if we do something that would stand out, carry out a demonstration that would make people think there was going to be some sort of explosion?'"
Mr Ibrahim's defence counsel, George Carter-Stephenson QC, asked if they had been talking about making real explosions.
The defendant replied: "No, just something like a firework, a firecracker - something that would make noise and cause panic."
He told the court that in November 2004 he and Mr Omar watched an hour-long video in Arabic about how to make a home-made hydrogen peroxide bomb.
Mr Ibrahim said: "I told Omar that we could use this for our demonstration. But I was thinking, at that stage, only to use a detonator."
He added: "When I saw how easy it is to make this stuff, [an] idea came into my head I could use it to make a fake explosive."
It never occurred to him to make anything other than a fake explosive, he said.
Mr Ibrahim added: "If you know how to make it, you can make it so as not to work if you have got enough information."
The jury was told that Ibrahim initially did not intend to detonate his home-made explosive.
"The device was going to be left unattended in a public place - that was the initial plan. We did not have any special (targets), just public places."
He went on: "We thought the police would take it seriously at the scene, but we thought that the scientists would conclude that it was fake, not real.
"I did not think I was going to be in trouble because it was just a hoax."
Mr Ibrahim said he had taken notes while watching the instruction video "many times" and decided to build a hydrogen peroxide-based explosive with a TATP detonator.
But he repeatedly insisted he had never intended the device to work.
When asked why he had tried to boil down the hydrogen peroxide to its optimum concentration for explosive, he replied "to make it as realistic as possible".
Mr Ibrahim said the device would not explode because there was no booster to help the TATP detonate the main charge.
He denied ever telling a flatmate, who can be identified only under the pseudonym Michael Bexhill, that he went to Pakistan to train for jihad, or holy war.
Mr Ibrahim told the court he had visited the country in 2004, but only for a holiday.
Mr Ibrahim is on trial with Mr Omar, 26, from New Southgate, north London; Manfo Kwaku Asiedu, 33, of no fixed address; Hussein Osman, 28, of no fixed address; Ramzi Mohammed, 25, of North Kensington, west London; and Adel Yahya, 24, of High Road, Tottenham, north London.