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Jan 09, 2012, 04:57 PM
Crash and learn

Need IC ID for DH9104/9100 TX schematic drawing

I drew the DH9104 Transmitter schematic diagram (49MHz).

The Printed Circuit Board is labelled "RoHS SH-9100T-01" so likely built for the DH9100 which means a lot of people here would be interested if I can figure out a way to post it.

But I need some help with the unlabelled controller Integrated Circuit.

Silan Semiconductors seems close, TX-2B & RX-2B CMOS LSI.

This is a 14 pin standard DIP with 5 separate proportional command inputs. Could be
five outputs from the controller IC sequencing the potentiometers into an ADC input.
Pins as follows:

(Pinout corrected - it helps to count from the top of the PCB)
01 - Through 100 ohm resister to Left/Right stick potentiometer
02 - Through 100 ohm resister to Back/Forard stick potentiometer
03 - Through 100 ohm resister to Back/Forard trim potentiometer
04 - +5v
05 - LED Display connector pin 3 (serial data or clock or analog)
06 - LED Display connector pin 4 (serial data or clock or analog)
07 - Voltage reference (or timing clock) 3.9K and 10K resistor divider
08 - Transmitter power amp On/Off keying
09 - Direct to Left/Right trim potentiometer
10 - Unused
11 - GND
12 - LED ground (switches LED On/Off)
13 - 100 ohm resister to Throttle stick potentiometer
14 - 0.1 ufd mylar to a 100 ohm resistor to all control commons

Display - 4 pin ribbon cable to daughter PCB 8 LED bar graph, displays throttle
9259051 - 14 pin DIP surface mount, part number too small for my eyes
Ribbon cable carries +5v, Gnd, SerialData, Clock. Or maybe analog voltage.

The simple Pierce 49MHZ crystal oscillator (maybe a FET) drives a simple keyed
power amplifier stage. Can't be more than a few milliwatts output.

The controller IC has too much smarts to be anything other than a
programmable controller or custom IC. If someone can tell me what it
is than I can draw the schematic in a logical manner. I am downloading
a Digikey catalog.

Please pass on to someone here who has recent knowledge with
programmable controllers. Its been a decade since I've built anything
with these things or even looked at data sheets.

When I get the transmitter pieces back to where it works again, I will hack the receiver Electronic Speed Contoller and Receiver.
Last edited by Ribble; Jan 12, 2012 at 11:48 PM.
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Jan 13, 2012, 12:34 AM
Crash and learn
Schematic redrawn and doesn't look too bad for hand-drawn. And if the scanner in my printer works, I should be able to post it.

My DH-9104 transmitter is re-assembled (sans a few miniature screws), but it works. Tried measuring the 49.860MHz frequency and determined you can't do it because the carrier is ON/OFF keyed and I don't see an easy way to turn the carrier on solid.

RF section looks close to this (a generic transmitter from around 2004)

And this (TX2B-RX2B chipset was popular)

Tried a few quick range checks.

And yes, the receiver was tuned with the antenna wrapped around the landing skid. So, if you unwrapped it, do a range check or just wrap it around the skid again. Made a big difference with mine wrapped again as it came out of the box. Wrapping the antenna like this (back and forth) causes the wrapped sections to cancel each other, making the 20 inch antenna act like a 7 inch antenna. But unwrapping it messes up the receiver.

I doubled my range by unwrapping the helicopter antenna, tied to the tail again, and retuned the receiver. My guess is tuning the receiver corrects the frequency more than matching the antenna.

Also tried shorting a diode in the transmitter to increase the power output, but made little difference.

On the transmitter, try connecting a 20 inch or longer piece of wire to the battery and let it hang out the bottom. Best on the battery negative (top right of battery pack). And range check (walk away with helicopter and try different orientations) while watching the LED on the Electronic Speed Control board.

counterpoise - the missing half of the transmitting antenna

Its almost 2am - time to walk to my spot in the park and fly again.
Last edited by Ribble; Jan 14, 2012 at 12:37 AM.
Jan 13, 2012, 11:57 PM
Crash and learn
My drafting skills and drafting kit are long lost.
Still, not too bad. Even looks balanced from 3 feet away.

Component values are best I could do. Not necessarily correct.

I'm thinking U2 sends a voltage out through each proportional
potentiometer one at a time and U2 pin 14 is a level comparator
that times how long it takes the mylar capacitor to discharge. A
poor mans Analog to Digital Converter (ADC).

Starting over with description of DH9104 transmitter.
Oscilloscope watching U2 Pin 8, external sync on control common.

It transmits at least 4 channels in 7 bit binary words which are 6 bits + parity bit. Channel resolution is therefore 1/64 meaning 64 possible proportional positions per channel.

Each binary bit is preceded by a short duration high state. Could be Non-Return-to-Zero (NRZ) scheme.

The transmitter time sequence (6 channel length binary words) is:
Proportional controls converted to digital, at same time transmitting long sync (RF keyed off).

1. - Transmits unknown binary word (always 011 0011)
2. - "LEFT/RIGHT TURN" knob value transmitted - Maybe controls Gyro gain. Full CCW = gyro weak.
3. - Rudder value transmitted.
4. - Throttle value transmitted.
5. - Elevator and "FORWARD/BACKWARDS" knob combined value transmitted.
6. - Checksum(?) transmitted last. Value changes with any control change.

The controls (Pots) are converted to a digital number by timing (or counting clock pulses) how long it takes to discharge a mylar capacitor.

"LEFT/RIGHT TURN" control counted up in binary as knob was turned clockwise (increases Gyro gain?)
000 0011 (lowest for that control)
000 0101
000 0110
000 1001
000 1010
000 1100
000 1111
001 0001
etc - 6 bits plus parity bit
101 0101 (highest for that control)

Transmitter remains keyed off if power turned on with throttle potentiometer not at minimum.

Vacant "CON6" connector is for external charging power. Hence diode D1 serves no purpose.
Transmitter works with only 3 alkaline 1.5v cells (4.5 volts).
Normal power is 8 alkaline cells (12 volts).
Unused U2 pin 10 dims the Bargraph LEDs.
U2 pins 5 and 6 (to bargraph display) quick pulse high when throttle moved. Display shows relative throttle position, blinks wildly when power on with throttle not at minimum.

Photos of newer receiver PCB

Tail and main are brushed motors.
Receiver ON/OFF switch only switches +5v. Motors and switching FETs remain energized.
Motor circuit - Battery B+ to motor connector, through motor, to motor connector, to switching FET, which shorts to B-, turns motor on.
Tail motor FET is closest to servo connector.
Snub diodes connected across motor connectors, white band to B+
+5 volt regulator between mounting screws, heat-sink tab is at +5v.
Gyro is vertical crystal-can at forward edge of PCB, with tape wrapped band. RATE MODE GYRO (not heading hold).
Rudder mixing (Gyro + throttle +rudder) is on receiver PCB. Tail motor tracks throttle. Gyro increases tail motor when nose left.

DH9104 Tail motor draws 2.99 amperes, that's 26 minutes calculated run time from 7.4v 1300mah Li-Ion battery.

Last edited by Ribble; Mar 03, 2012 at 12:17 AM.
Jan 14, 2012, 01:20 AM
Crash and learn
The hard part was figuring out what it was after I got it on paper.

The DH-9104 receiver is next and those parts are so much smaller.
Mar 27, 2012, 06:02 AM
Registered User
Originally Posted by Ribble
The hard part was figuring out what it was after I got it on paper.

The DH-9104 receiver is next and those parts are so much smaller.
Possible I not good seen in diagramm, but where is antenne for receiver?
Mar 27, 2012, 10:02 AM
Crash and learn
Didn't do the receiver. It is a double sided printed circuit board with much of the copper traces hidden under components. Many components have no part number or are impossible to read.

Some of it I understand. My DH9104 needs the receiver to fly and I don't want to damage it.
Apr 04, 2012, 06:34 PM
Crash and learn
fly4fun6719 pulled a part number off one of the DH9104 motor switching FETs.
Part number is: CEP73A3G

N-Channel Enhancement Mode Field Effect Transistor
30V, 62A,
RDS(ON) = 9mW @VGS = 10V
RDS(ON) = 16mW @VGS = 4.5V.
Super high dense cell design for extremely low RDS(ON).

"Purchased a IRF1405 mosfet from the local electronics store and fitted it..I tried it with the receiver out of the helicopter and it appears to work ok.The only problem I had was removing the original mosfet. I haven't done this sought of work for some years and I am a bit rusty."

IRF1405 should work as a replacement for any Syma or Double Horse receiver board.
Note: Input control Voltage Gate to Source is 5.0v for 20 amps motor current, though it does start switching ON between 2.0 and 4.0 Volts.

VDSS = 55V
RDS(on) = 5.3mΩ
ID = 169A

DH9104 tail motor was 2.99 amps full speed off 7.4v 1300mah Li-Ion stock battery.

Main motor 5.72 amps full speed off 7.4v 1300mah Li-Ion stock battery.

Non-motor load = 23ma = receiver and forward white floodlight LED (Transmitter turned off)
Receiver without LED and motors = 16.1ma (Transmitter turned off)
Receiver without LED and motors = 17.6ma (Transmitter turned on)
Receiver without LED and motors, Servo disconnected = 9.6ma (Transmitter turned off)
Receiver without LED and motors, Servo disconnected = 11.2ma (Transmitter turned on)

7.4v 1300mah Li-Ion stock battery = 7.67 volts no load after running tests (needs recharging).

I had expected main motor around 10 amps. It may not have been running full speed due to the test leads, but the main blades were bending upwards, so 5.72 amps is at least close.

Motor ampere measurements were by shorting motor switching FETs to ground through ammeter. Kids, don't do this at home!
Last edited by Ribble; Apr 04, 2012 at 07:07 PM.
May 31, 2012, 11:00 PM
Registered User


Hi ribble can u help me i have doble horse 9100 I thing the receiver is the same of 9104 49 MHz send u pic with my problem
I need to know howmany turns and wire size
Thank you sorry my english
Jun 01, 2012, 12:53 AM
Crash and learn
My DH9104 also on 49MHz.

Looks like 2 1/2 turns #32 wire on 4mm diameter core with 3mm diameter tuning slug. The coil wire is 3mm high. Appears to be a series tuned circuit which has a very sharp (not broad) RF peak.

Used #30 wire-wrap wire to compare to and coil wire looks slightly thinner.

Without a coil form, I would make a same size open coil with #30 wire and tune it by changing distance between windings. Instead of a vertical coil, solder it in horizontally and use a toothpick to tune it while increasing range. Unscrew the transmitter antenna and walk helicopter away from transmitter.

I've done this many times (other projects) and it works very well, surprisingly well. But you would have to melt wax on it before or after tuning or some other means of keeping shape during crashes.

Since you will be tuning the coil, unwrap the antenna and attach to tail. They come tuned with antenna wrapped around skid.
Last edited by Ribble; Jun 01, 2012 at 01:07 AM.
Jun 09, 2012, 04:17 PM
Registered User
Hi mister ribble that circuit work in FM or Am
Jun 09, 2012, 08:04 PM
Crash and learn
I would call it continuous wave. The DH9104 transmitter is ON/OFF keying of the RF carrier. Likely 1970's technology. At least it uses a crystal to determine frequency.

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