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GM5: Least-cost USB-MIDI Interface Chip for 4.50 EUR


TK.
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Getting half my house blown up kinda set the process of finishing the PCB back a couple of days. I'm back on it though!

Now there's dedication! Get yourself sorted out before you worry about the PCB's, I think everybody here understands that exploding houses can cause delays!

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When did this transition occur?

I'm using the evaluation board from Ploytec...

TK, what have you think for a date to sell the Chips?

1) we've to wait until the PCB layout is ready

2) thereafter I've to ask Ploytec for a confirmation, that they handle the PCB order for us

3) thereafter I can tell you the exact prices (+ taxes and shipping)

4) thereafter I need the final quantity numbers for GM5/PCBs from your side

5) I will collect the money and order the chips and PCBs (maybe in parallel, if most people prepayed fast enough)

6) I (and maybe also Screaming_Rabbit) will send you chips/PCBs once they are available

It can be assumed, that we will order 500 chips. Everybody who is already in the list will get the requested quantity

Note that we have to order n x 100 PCBs!

Best Regards, Thorsten.

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Another good news: Ploytec offered the possibility to layout our own PCB, Nils is working on it. :)

The PCB should have the same size like the original Ploytec evaluation board, otherwise we would have to pay more money for additional area - therefore the focus is to make it more DIY friendly (e.g. replacing SMD resistor/caps by through-hole parts)

I happen to like soldering chip resistors and caps, especially if there are already some surface mount components on a board.  I am a big fan of component footprints that can accomodate chip components as well as thru-hole.  (I know I'm in the minority, but just wanted to throw that in)

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No Problem! :)

Status Update: the layout is finished, and Ploytec will organize a sample, so that I can test the PCB before 400 pieces will be ordered:

mbhp_usb_gm5_v1_1.gif

(/edit: final v1.1 version)

I've also already ordered 500 GM5 chips.

Atmel has a lead time of up to 14 weeks, therefore it could take a while - we've enough time to collect the money (more details about the final prices and the procedure soon)

Best Regards, Thorsten.

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just a question, i've been pondering on for a little while...if we wanted status leds on the outside of the box for the midi ins and outs. how would it be best to do that? i've been thinking about adding another optocoupler on the ins and outs and then a transistor (taking input from the output of the optocoupler) to power the led itself. Is this a workable solution?

Cheers Chris.

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Is it too late to jump in on this one? Or is it unlikely that we'll make it to the 750-chip level to qualify for another order?

There are many people that ordered too much (like myself)

So you won't miss the boat. Just ask again when everyone has their stuff.

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There are many people that ordered too much (like myself)

So you won't miss the boat. Just ask again when everyone has their stuff.

That's what I thought I'd probably have to do. No biggie really, I'll just keep an eye on the Fleamarket  ;)

/Edited for my poor attempt at spelling.

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i've been thinking about adding another optocoupler on the ins and outs and then a transistor (taking input from the output of the optocoupler) to power the led itself...

Hi Chris,

You definitely don't need any additional optocouplers to do this. The optocoupler is really just to 'couple' the input. You can think of the optocoupler as an LED and a photodiode/phototransistor within an enclosed package. The input drives the LED, which is optically coupled to the photodiode/phototransistor. When current runs in the input line, the LED transmits light to the photodiode/phototransistor, which is then connected to the UART input.

Optocoupled inputs have some useful properties:

-Isolation of potentially damaging electrical energy

-Elimination of ground loops

-Rejection of common mode noise

(have I missed anything?)

Depending on the circuit, there may be somewhere you can directly connect a resistor & LED. Otherwise, it is quite likely possible that you could tap a FET onto the signal you are monitoring, which drives an LED with a current limiting resistor. The gate of a FET provides a high impedance input, so it generally won't create any appreciable loading on a digital signal line.

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Hey Madox and TK,

thanks for your input on this, I will definitely look into both options as we come up to buying, building and finishing this project.

madox: I was mainly using the Optocouplers for that reason, which makes the fets perfect (no loading on the signal line!).

TK: I had a look at the LTC before, and noticed that part of design, however i didn't look to deeply, so i will have a dig and see what i understand.

anyway cheers Chris.

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No probs Chris.

Gnerally with this sort of thing, most digital inputs will have a high input impedance, and digital outputs will have pretty low output impedance. FET inputs have some capacitance, which requires a small switching current during digital transitions, and only a very small quiescent current.

Although many IC outputs won't have a large current sourcing capability, the input stages they are driving are so low as to allow the connection of multiple gates.

Midi frequencies are also relatively low compared to what modern IC's are often designed to handle, which simplifies such connections.

To evaluate specific design ideas, you can look at device data sheets to see what current drive and sinking to expect. Connecting multiple gates to an output places the input impedances in parallel. For this kind of application, very simple linear circuit theorems should be fine to see what is happening electrically.

I will also have a look at the "In/Out indicator circuit of the MBHP_LTC", as TK suggested, as I am planning to design my own MIDI interface with these GM5 chips. I'm guessing this is just some CMOS gates on an IC, which will be performing the same function as the FET I described. Using IC's like this, will usually simplify the connection of multiple LED's, such as one for each input/output.

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Status Update:

   - GM5 chips will be available end of July.

   - I will get the PCB Prototype this or next week. I already got 5 new GM5 samples with most recent firmware for testing

   - money will be collected once I know the exact delivery dates for GM5 and PCBs

Best Regards, Thorsten.

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mbhp_usb_gm5_proto.jpg

Unfortunately I swapped the MIDI In/Out labels, accordingly MIDI In and Out jack traces are connected to the wrong pins. It's easy to fix, but very annoying anyhow. Good that we ordered a prototype ;)

Best Regards, Thorsten.

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