Replace the GE LOGIQ a200 ultrasound measurement key with a self-made touch switch

A GE LOGIQ a200 ultrasound machine often breaks down its "measurement key" due to frequent use. However, since the measurement key is very expensive and difficult to buy, the key was previously repaired by removing the spring inside the infrequently used key.

As the number of times the key is replaced increases, there is no key available for replacement. Can a key with a longer life be used as a replacement? A commonly used touch switch was used as a substitute, but the life is too short (usually it must be replaced within 3 days) and it is not beautiful, so this method does not work.

After careful analysis, it is believed that using a touch switch to replace the measurement key of the original B-ultrasound machine should have the longest life; under the premise of no impact on the original B-ultrasound machine circuit, the touch switch circuit schematic diagram is selected as shown in the attached figure.

In the attached circuit, IC1 (NE555) time base integrated circuit is designed as a monostable circuit to perform pulse shaping on the electrical signal input from pin ②. The monostable time can be adjusted by changing the values ​​of R1 and C1. When the "sensing touch sheet" is touched by hand, the stray electrical signal of the human body is introduced into pin ② of IC1 time base circuit through the touch sheet, R3 and R4, and its pin ③ outputs a high level, which makes the light-emitting diode in the photocoupler emit light through R5, and the phototransistor inside it is turned on (equivalent to the "measurement key" of the original B-ultrasound machine being closed). Then the circuit charges Cl through Rl. When the potential of pin ⑥ exceeds 6V (2/3VCC), the output of pin ③ of the time base circuit jumps to a low level, and the phototransistor in IC2 is cut off (equivalent to the "measurement key" of the original B-ultrasound machine being disconnected), thus completing an on/off operation. After actual use, the touch switch circuit has no effect on the original B-ultrasound machine circuit after replacing the measurement key of the B-ultrasound machine. In addition, if you do not want to add an additional power supply to the self-made touch switch circuit, you can also use the 4.8V power supply inside the original B-mode ultrasound machine keyboard, but this may increase the power supply burden of the original circuit (but the sensitivity of the touch switch can be readjusted, that is, the value of R2 can be increased or the value of R3/R4 can be reduced). The successful experiment of this circuit can solve the life problem of the B-mode ultrasound key of this model.

For easy operation, the output of the self-made touch switch is connected to the measuring key of the original B-ultrasound machine in the form of a connector. The method is to weld a 2-core DuPont wire from the two electrical contacts of the original measuring key: and weld a 2-pin socket at the output end of the touch switch. Just plug the DuPont wire into this socket.

Note that B-mode ultrasound is a precision instrument. Before soldering, it is best to unplug the cable connecting the keyboard and the host to disconnect the electrical connection between the keyboard and the host. In addition, when soldering, it is best to unplug the power supply of the soldering iron and use the residual heat to solder, or reliably ground the soldering iron! This is to prevent static electricity from damaging the components in the circuit of the B-mode ultrasound machine.