Carrier board for A10 Lime

Started by oldpenguin, September 12, 2014, 01:57:29 pm

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I'm studying the viability of a carrier board to connect on top of the A10 Lime (or below if you turn the A10 over  ;) ).
My question are?
1. Can you expect the connectors to always be located at the same exact place (I mean not much deviation from one production batch to another) ?
I ask this because these are SMT connectors and I presume they are placed automatically by a p&p machine, but can suffer some position change during soldering. Correct me if I'm wrong.
2. Where are the exact coordinates of pin 1 of each GPIO connector ?


Robert Leacroft

The header connectors that are fitted to the lime and also the mating sockets that Olimex sell are indeed SMT but they all have two plastic pegs on the back that fit into two 0.8 mm holes. These peg/holes ensure that the connectors are mounted in the correct position and held still whilst they are soldered. The pegs can just be seen on the Olimex "buy it" pages.

I have just made an intermediate pcb using the smt 1.27mm sockets from Olimex on one side and tall thru-hole  2.54 mm pitch sockets on the other side. This pcb just covers the area of the Limes GPIO connectors and sits down low. I have just brought out GPIO1 GPIO2 and GPIO4 (for audio) and then another pcb with my actual circuit on it fits on top of this intermediate board and thus clears all of the other tall components and it can be as big as it needs to be. The use of this intermediate 1.27 to 2.54 pcb gets around the problem that no one seems to make 1.27mm connectors that are tall enough to clear the rest of the Lime components.

I imported the Lime Eagle pcb  layout into my own pcb package to line up the connectors and their peg holes to my intermediate pcb. On making the board and hand soldering the smt sockets they dropped straight on to the Lime absolutely perfectly. I can modify and experiment with my main circuit pcb without worrying about positions on the Lime at all.



Hello Robert

Thank you for your reply.
You are quite right about the connectors. I didn't notice, but the pegs are visible on the underside of the Lime board.
I see the difficulty of making a carrier board directly connected to the Lime because of the height of the connectors. If connected directly, it is necessary to leave some"holes" for the tall components like the RJ45 and USB connectors, which is not very practical.
The idea of the intermediate carrier is good, but I need to bring up the LCD connector preferably to the Olimex compatible 40 pin 2,54mm version, so I guess I will have to study how large this intermediate board might become.
I like your idea of importing the Lime pcb design, but Olimex could publish the connector coordinates, especially the distance to the mounting holes. It would ease the work if you work with other CAD systems (which is my case). I will try the free version anyway.