{"action":"created","issue":{"url":"https://api.github.com/repos/poppy-project/pixl/issues/1","repository_url":"https://api.github.com/repos/poppy-project/pixl","labels_url":"https://api.github.com/repos/poppy-project/pixl/issues/1/labels{/name}","comments_url":"https://api.github.com/repos/poppy-project/pixl/issues/1/comments","events_url":"https://api.github.com/repos/poppy-project/pixl/issues/1/events","html_url":"https://github.com/poppy-project/pixl/issues/1","id":143216858,"number":1,"title":"Suggestion: simplify the board","user":{"login":"sonelu","id":7189445,"avatar_url":"https://avatars.githubusercontent.com/u/7189445?v=3","gravatar_id":"","url":"https://api.github.com/users/sonelu","html_url":"https://github.com/sonelu","followers_url":"https://api.github.com/users/sonelu/followers","following_url":"https://api.github.com/users/sonelu/following{/other_user}","gists_url":"https://api.github.com/users/sonelu/gists{/gist_id}","starred_url":"https://api.github.com/users/sonelu/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/sonelu/subscriptions","organizations_url":"https://api.github.com/users/sonelu/orgs","repos_url":"https://api.github.com/users/sonelu/repos","events_url":"https://api.github.com/users/sonelu/events{/privacy}","received_events_url":"https://api.github.com/users/sonelu/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":1,"created_at":"2016-03-24T11:02:17Z","updated_at":"2016-03-24T12:03:07Z","closed_at":null,"body":"Hi guys,\r\n\r\nI really like this board - I'm not sure I understand how is possible this works (... with the OE on the 126 being controlled by the TX from the UART) but if indeed this is working I have the following two suggestions for simplification:\r\n\r\n- instead of all the circuit in the top part of the diagram (the switching power regulator) I suggest you use a Murata ready made one. You can find it [here](http://uk.rs-online.com/web/p/non-isolated-dc-dc-converters/7962138/). That should save you for a lot of trouble and I think it might be even cheaper.\r\n\r\n- instead of using the two MOSFET for the TX line (you use that as a level shifter isn't?) why not use another 1T126 gate that is powered at 5V with the OE on VCC (always on?)\r\n\r\nAlso it might be a good idea to put also a MOLEX SPOX connector (like the one in the AX series) so that the board can be used with those servos too. Obviously you will need to warn the people that they cannot mix the two together. Better leave the connector not soldered and let the people solder the version they want - you will need to have the holes oval to accommodate the difference in pitch between the XL and AX connectors (similar to what Robotis did on the OpenCM9.04).\r\n\r\nLet me know what you think."},"comment":{"url":"https://api.github.com/repos/poppy-project/pixl/issues/comments/200804879","html_url":"https://github.com/poppy-project/pixl/issues/1#issuecomment-200804879","issue_url":"https://api.github.com/repos/poppy-project/pixl/issues/1","id":200804879,"user":{"login":"nicolas-rabault","id":9554146,"avatar_url":"https://avatars.githubusercontent.com/u/9554146?v=3","gravatar_id":"","url":"https://api.github.com/users/nicolas-rabault","html_url":"https://github.com/nicolas-rabault","followers_url":"https://api.github.com/users/nicolas-rabault/followers","following_url":"https://api.github.com/users/nicolas-rabault/following{/other_user}","gists_url":"https://api.github.com/users/nicolas-rabault/gists{/gist_id}","starred_url":"https://api.github.com/users/nicolas-rabault/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/nicolas-rabault/subscriptions","organizations_url":"https://api.github.com/users/nicolas-rabault/orgs","repos_url":"https://api.github.com/users/nicolas-rabault/repos","events_url":"https://api.github.com/users/nicolas-rabault/events{/privacy}","received_events_url":"https://api.github.com/users/nicolas-rabault/received_events","type":"User","site_admin":false},"created_at":"2016-03-24T12:03:07Z","updated_at":"2016-03-24T12:03:07Z","body":"The main problem with the Raspberry Pi is the no real time linux, we can't manage a direction flag easily. So we have to do it automatically by hardware. Here the main idea is to keep the system always on RX mode but if we have a 0 on the TX output of the RPI we stop the RX mode to avoid any echo. The is not perfect because we can see smal perturbation on the RX side during a transmition, but the RPI deal with it easily...\r\n\r\nWe design our power circuit with webench, and we don't have any trouble with it. The BOM for this part is pretty good (~1$) and performances and footprind is good. I keep your good reference in mind if we have any trouble or for other boards!\r\n\r\nYour suggestion about the two mosfet for TX is completely exact. These mosfet are probably the biggest limitation of this board because we have a leakage curent passing on it. This leakage current probably limit the number of device on the bus. Actually we try to improve it for the design of another board called Hipi. We probably don't change the Pixel right now because she fit for our need (poppy-ergo-jr) and we start the production process. This board is really dedicated to Poppy-ergo-jr robot, the Hipi will be better other applications!\r\n\r\n Your idea about oval hole is really cool! I never note it from OpenCM9.04, we will do it!\r\n\r\nThank you for your great contribution!"}}