BB MACHINEGUN OWNERS GROUP FORUMS - If It Does Not Shoot Metal It Does Not Belong Here :: DROZD MP661K BB Machinegun Owners Group Discussion Forum :: Drozd Blackbird "Sergey's board - 2" (9-24V, 400-2000 RPM, Full auto, 4-12 ms)

Greetings Gentlemen.

Please welcome the board ver.3 (Sergey's board - 2).

What it inherits from the previous design:
1. The same size and controls positions.
2. Power supply range (9-24 V).
3. Drozd/backbird compatibility.

What's new:
1. ROF: 400-600-800-1000-1200-1400-1600-1800-2000.
2. Mag voltage is controlled with a jumper (see below).
3. Better transistor in mag control circuit.
4. Pulse: 4-12 mS.
5. It's $10 cheaper (no need for DC-DC converter).

Here's the ideology behind the design changes: let's say good bye to DC-DC converter, we don't need it any more. Originally, it was implemented because we needed to lower mag voltage from 24 to 9 volts with minimum losses. DC-DC converters are efficient when there is significant difference between input and output voltages. But then I had to increase its output voltage from 9 to 14 volts (so in-out difference was reduced). Now, achieving higher ROFs requires further voltage increase, plus higher voltage applied to the mag means the converter has to supply more current. This would mean less efficient and more bulky DC-DC converter. The processor and LED display draw only 5-12 mA so a simple linear voltage regulator can supply them with all they need. As for the mag, you have three options now:

1. If your batteries voltage is below 17.5 volts you can put the jumper in the position closer to the mag connector (there are two positions available, see the photo below). This means the mag voltage regulator is bypassed and all batteries voltage is applied to mag motor. The actual RPM you'll be able to achieve in this mode depends on your batteries voltage.

2. If your batteries voltage exceeds 17.5 volts and the jumper is in the position closer to the display, mag voltage is limited to 15 volts. This mode is safe for Blackbird-type magazines. The actual RPM you'll be able to achieve depends on your mag type and condition, let's wait for users feedback. If your batteries voltage is above 20 volts please check the linear regulator temperature after 3-5 minutes of intense shooting. If you tend to use 20-24 V batteries and a mag requiring much current, you may need to mount a heatsink on the part, there is enough space for it.

3. If you want to achieve maximum RPM, just move the jumper to the position closer to the mag connector. All batteries voltage is applied to your mag now. The new transistor on the board can cope with increased current. No need to check voltage regulator temperature in this mode.

Here's the jumper location:

It's possible to use three wires to connect an external switch to the plugs on the board and use it instead of the jumper.

As I don't need to make DC-DC converter any more, the new board price is reduced to USD 120.

Here's my contact info:
E-mail: e-go@inbox.ru
Skype: sergey.pismensky
Phone: +7-950-177-2500.

Yours,
Sergey Pismensky.
[1 edits; Last edit by Sergey_new_pcb at 09:18:46 Thu Apr 14 2011]

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